Enhance common launch instance helper

Move retry logic to the launch single guest method.

Add optional arguments that is passed on to the downstream launch
guest helper.

zaza/openstack/charm_tests/test_utils.py

@@ -526,7 +526,8 @@ class OpenStackBaseTest(BaseCharmTest):
             # Test did not define self.RESOURCE_PREFIX, ignore.
             pass
 
-    def launch_guest(self, guest_name, userdata=None):
+    def launch_guest(self, guest_name, userdata=None, use_boot_volume=False,
+                     instance_key=None):
         """Launch two guests to use in tests.
 
         Note that it is up to the caller to have set the RESOURCE_PREFIX class
@@ -539,9 +540,14 @@ class OpenStackBaseTest(BaseCharmTest):
         :type guest_name: str
         :param userdata: Userdata to attach to instance
         :type userdata: Optional[str]
+        :param use_boot_volume: Whether to boot guest from a shared volume.
+        :type use_boot_volume: boolean
+        :param instance_key: Key to collect associated config data with.
+        :type instance_key: Optional[str]
         :returns: Nova instance objects
         :rtype: Server
         """
+        instance_key = instance_key or glance_setup.LTS_IMAGE_NAME
         instance_name = '{}-{}'.format(self.RESOURCE_PREFIX, guest_name)
 
         instance = self.retrieve_guest(instance_name)
@@ -554,10 +560,16 @@ class OpenStackBaseTest(BaseCharmTest):
                 instance.id,
                 msg="server")
 
-        return configure_guest.launch_instance(
-            glance_setup.LTS_IMAGE_NAME,
-            vm_name=instance_name,
-            userdata=userdata)
+        for attempt in tenacity.Retrying(
+                stop=tenacity.stop_after_attempt(3),
+                wait=tenacity.wait_exponential(
+                    multiplier=1, min=2, max=10)):
+            with attempt:
+                return configure_guest.launch_instance(
+                    instance_key,
+                    vm_name=instance_name,
+                    use_boot_volume=use_boot_volume,
+                    userdata=userdata)
 
     def launch_guests(self, userdata=None):
         """Launch two guests to use in tests.
@@ -572,15 +584,10 @@ class OpenStackBaseTest(BaseCharmTest):
         """
         launched_instances = []
         for guest_number in range(1, 2+1):
-            for attempt in tenacity.Retrying(
-                    stop=tenacity.stop_after_attempt(3),
-                    wait=tenacity.wait_exponential(
-                        multiplier=1, min=2, max=10)):
-                with attempt:
-                    launched_instances.append(
-                        self.launch_guest(
-                            guest_name='ins-{}'.format(guest_number),
-                            userdata=userdata))
+            launched_instances.append(
+                self.launch_guest(
+                    guest_name='ins-{}'.format(guest_number),
+                    userdata=userdata))
         return launched_instances
 
     def retrieve_guest(self, guest_name):