Fix use of ``openstack-release`` to determine codename

The current code will oportunisticly attempt to install the
``openstack-release`` package, but it does so without configuring
the UCA sources.

Attempt to configure sources to avoid charms getting stuck in a
chicken and egg situation.

Closes-Bug: #1951462
Change-Id: I8ed6e2dfc7ce83c2e56fd072458e2ef189968e41

charms_openstack/charm/core.py

@@ -1204,11 +1204,17 @@ class BaseOpenStackCharmActions(object):
         :raises: AttributeError, ValueError
         """
 
-        codename = os_utils.get_installed_os_version()
-        if codename:
-            return codename
-
         try:
+            # The purpose of the UCA ``openstack-release`` package is to
+            # relieve the charm and test code from maintining version maps.
+            #
+            # The ``get_installed_os_version`` helper will attempt to install
+            # it, and that can only happen if the UCA is configured first.
+            self.configure_source()
+            codename = os_utils.get_installed_os_version()
+            if codename:
+                return codename
+
             vers = self.get_package_version(
                 package,
                 apt_cache_sufficient=apt_cache_sufficient)

unit_tests/charms_openstack/charm/test_core.py

@@ -902,12 +902,14 @@ class TestMyOpenStackCharm(BaseOpenStackCharmTest):
         self.patch_object(chm_core.os_utils, 'get_installed_os_version')
         self.get_installed_os_version.return_value = None
         self.upstream_version.return_value = '3.0.0~b1'
+        self.patch_object(self.target, 'configure_source')
         self.assertEqual(
             self.target.get_os_codename_package(
                 'testpkg', codenames),
             'newton')
         self.upstream_version.assert_called_once_with(
             pkg_mock.current_ver.ver_str)
+        self.configure_source.assert_called_once()
         self.upstream_version.reset_mock()
         self.assertEqual(
             self.target.get_os_codename_package(