Add a way to compare OS release pair

It was a functionality available in charm helpers. It is implemented in
a similar way:
* Get the current series from the `keystone` machine
* Get the OS version from `get_current_os_versions`
* Try to find the built string in `OPENSTACK_RELEASES_PAIRS`
It is thus possible to compare release pairs as it returns integers.

.gitignore

@@ -5,5 +5,6 @@ dist/
 .local
 zaza.egg-info/
 .coverage
+.vscode/
 # Sphinx
 doc/build

unit_tests/utilities/test_zaza_utilities_openstack.py

@@ -645,3 +645,72 @@ class TestOpenStackUtils(ut_utils.BaseTestCase):
         with self.assertRaises(exceptions.NeutronBGPSpeakerMissing):
             openstack_utils.neutron_bgp_speaker_appears_on_agent(
                 _neutronclient, 'FAKE_AGENT_ID')
+
+    def test_get_current_openstack_release_pair(self):
+        self.patch(
+            'zaza.utilities.openstack.get_current_os_versions',
+            new_callable=mock.MagicMock(),
+            name='_get_os_version'
+        )
+        self.patch(
+            'zaza.utilities.juju.get_machines_for_application',
+            new_callable=mock.MagicMock(),
+            name='_get_machines'
+        )
+        self.patch(
+            'zaza.utilities.juju.get_machine_status',
+            new_callable=mock.MagicMock(),
+            name='_get_machine_status'
+        )
+
+        # No machine returned
+        self._get_machines.return_value = []
+        with self.assertRaises(exceptions.NoKeystoneFound):
+            openstack_utils.get_current_os_release_pair()
+
+        # No series returned
+        self._get_machines.return_value = ['6']
+        self._get_machine_status.return_value = None
+        with self.assertRaises(exceptions.SeriesNotFound):
+            openstack_utils.get_current_os_release_pair()
+
+        # No OS Version returned
+        self._get_machine_status.return_value = 'xenial'
+        self._get_os_version.return_value = {}
+        with self.assertRaises(exceptions.OSVersionNotFound):
+            openstack_utils.get_current_os_release_pair()
+
+        # Normal scenario
+        self._get_os_version.return_value = {'keystone': 'mitaka'}
+        expected = 'xenial_mitaka'
+        result = openstack_utils.get_current_os_release_pair()
+        self.assertEqual(expected, result)
+
+    def test_get_openstack_release(self):
+        self.patch(
+            'zaza.utilities.openstack.get_current_os_release_pair',
+            new_callable=mock.MagicMock(),
+            name='_get_os_rel_pair'
+        )
+
+        # Bad release pair
+        release_pair = 'bad'
+        with self.assertRaises(exceptions.ReleasePairNotFound):
+            openstack_utils.get_os_release(release_pair)
+
+        # Normal scenario
+        expected = 4
+        result = openstack_utils.get_os_release('xenial_mitaka')
+        self.assertEqual(expected, result)
+
+        # Normal scenario with current release pair
+        self._get_os_rel_pair.return_value = 'xenial_mitaka'
+        expected = 4
+        result = openstack_utils.get_os_release()
+        self.assertEqual(expected, result)
+
+        # We can compare releases xenial_queens > xenial_mitaka
+        xenial_queens = openstack_utils.get_os_release('xenial_queens')
+        xenial_mitaka = openstack_utils.get_os_release('xenial_mitaka')
+        release_comp = xenial_queens > xenial_mitaka
+        self.assertTrue(release_comp)

zaza/utilities/exceptions.py

@@ -29,3 +29,27 @@ class NeutronBGPSpeakerMissing(Exception):
     """No BGP speaker appeared on agent."""
 
     pass
+
+
+class NoKeystoneFound(Exception):
+    """No Keystone found in machines."""
+
+    pass
+
+
+class SeriesNotFound(Exception):
+    """Series not found in status."""
+
+    pass
+
+
+class OSVersionNotFound(Exception):
+    """OS Version not found."""
+
+    pass
+
+
+class ReleasePairNotFound(Exception):
+    """Release pair was not found in OPENSTACK_RELEASES_PAIRS."""
+
+    pass

zaza/utilities/openstack.py

@@ -6,6 +6,7 @@ from .os_versions import (
     OPENSTACK_CODENAMES,
     SWIFT_CODENAMES,
     PACKAGE_CODENAMES,
+    OPENSTACK_RELEASES_PAIRS,
 )
 
 from glanceclient import Client as GlanceClient
@@ -1123,6 +1124,52 @@ def get_application_config_keys(application):
     return list(application_config.keys())
 
 
+def get_current_os_release_pair():
+    """Return OpenStack Release pair name.
+
+    :returns: Name of the OpenStack release pair
+    :rtype: str
+    :raises: exceptions.NoKeystoneFound
+    :raises: exceptions.SeriesNotFound
+    :raises: exceptions.OSVersionNotFound
+    """
+    keystone = juju_utils.get_machines_for_application('keystone')
+    if len(keystone) >= 1:
+        keystone = keystone[0]
+    else:
+        raise exceptions.NoKeystoneFound()
+
+    series = juju_utils.get_machine_status(keystone, key='series')
+    if not series:
+        raise exceptions.SeriesNotFound()
+
+    os_version = get_current_os_versions(['keystone']).get('keystone')
+    if not os_version:
+        raise exceptions.OSVersionNotFound()
+
+    return '{}_{}'.format(series, os_version)
+
+
+def get_os_release(release_pair=None):
+    """Return index of release in OPENSTACK_RELEASES_PAIRS.
+
+    :returns: Index of the release
+    :rtype: int
+    :raises: exceptions.ReleasePairNotFound
+    """
+    if release_pair is None:
+        release_pair = get_current_os_release_pair()
+    try:
+        index = OPENSTACK_RELEASES_PAIRS.index(release_pair)
+    except ValueError:
+        msg = 'Release pair: {} not found in {}'.format(
+            release_pair,
+            OPENSTACK_RELEASES_PAIRS
+        )
+        raise exceptions.ReleasePairNotFound(msg)
+    return index
+
+
 def get_application_config_option(application, option):
     """Return application configuration.
 

zaza/utilities/os_versions.py

@@ -37,6 +37,12 @@ OPENSTACK_CODENAMES = OrderedDict([
     ('2018.1', 'queens'),
 ])
 
+OPENSTACK_RELEASES_PAIRS = [
+    'trusty_icehouse', 'trusty_kilo', 'trusty_liberty',
+    'trusty_mitaka', 'xenial_mitaka', 'xenial_newton',
+    'yakkety_newton', 'xenial_ocata', 'zesty_ocata',
+    'xenial_pike', 'artful_pike', 'xenial_queens',
+    'bionic_queens', 'bionic_rocky', 'cosmic_rocky']
 
 # The ugly duckling - must list releases oldest to newest
 SWIFT_CODENAMES = OrderedDict([