Make get_current_os_release_pair variable

It is possible to use `get_current_os_release_pair` with an argument or
to use the default one (`keystone`)

unit_tests/utilities/test_zaza_utilities_openstack.py

@@ -680,7 +680,13 @@ class TestOpenStackUtils(ut_utils.BaseTestCase):
         with self.assertRaises(exceptions.OSVersionNotFound):
             openstack_utils.get_current_os_release_pair()
 
-        # Normal scenario
+        # Normal scenario, argument passed
+        self._get_os_version.return_value = {'keystone': 'mitaka'}
+        expected = 'xenial_mitaka'
+        result = openstack_utils.get_current_os_release_pair('keystone')
+        self.assertEqual(expected, result)
+
+        # Normal scenario, default value used
         self._get_os_version.return_value = {'keystone': 'mitaka'}
         expected = 'xenial_mitaka'
         result = openstack_utils.get_current_os_release_pair()

zaza/utilities/openstack.py

@@ -1124,26 +1124,28 @@ def get_application_config_keys(application):
     return list(application_config.keys())
 
 
-def get_current_os_release_pair():
+def get_current_os_release_pair(application='keystone'):
     """Return OpenStack Release pair name.
 
+    :param application: Name of application
+    :type application: string
     :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]
+    machines = juju_utils.get_machines_for_application(application)
+    if len(machines) >= 1:
+        machine = machines[0]
     else:
         raise exceptions.NoKeystoneFound()
 
-    series = juju_utils.get_machine_status(keystone, key='series')
+    series = juju_utils.get_machine_status(machine, key='series')
     if not series:
         raise exceptions.SeriesNotFound()
 
-    os_version = get_current_os_versions(['keystone']).get('keystone')
+    os_version = get_current_os_versions([application]).get(application)
     if not os_version:
         raise exceptions.OSVersionNotFound()