Purge old packages on upgrade-charm

On charm upgrade the charm may switch to py3 packages. If so, ensure
the old py2 packages are purged. If the purge occurs then restart
services.

Change-Id: I984a227b3fe12a0086c926ae69c27d6e4d9741d3
Closes-Bug: 1803451

hooks/nova_cc_hooks.py

@@ -951,6 +951,12 @@ def upgrade_charm():
     ch_fetch.apt_install(
         ch_fetch.filter_installed_packages(
             ncc_utils.determine_packages()), fatal=True)
+    packages_removed = ncc_utils.remove_old_packages()
+    if packages_removed:
+        hookenv.log("Package purge detected, restarting services", "INFO")
+        for s in ncc_utils.services():
+            ch_host.service_restart(s)
+
     for r_id in hookenv.relation_ids('amqp'):
         amqp_joined(relation_id=r_id)
     for r_id in hookenv.relation_ids('identity-service'):

hooks/nova_cc_utils.py

@@ -395,6 +395,19 @@ def determine_purge_packages():
     return []
 
 
+def remove_old_packages():
+    '''Purge any packages that need ot be removed.
+
+    :returns: bool Whether packages were removed.
+    '''
+    installed_packages = ch_fetch.filter_missing_packages(
+        determine_purge_packages())
+    if installed_packages:
+        ch_fetch.apt_purge(installed_packages, fatal=True)
+        ch_fetch.apt_autoremove(purge=True, fatal=True)
+    return bool(installed_packages)
+
+
 def save_script_rc():
     env_vars = {
         'OPENSTACK_PORT_MCASTPORT': hookenv.config('ha-mcastport'),
@@ -547,11 +560,7 @@ def _do_openstack_upgrade(new_src):
     ch_utils.reset_os_release()
     ch_fetch.apt_install(determine_packages(), fatal=True)
 
-    installed_pkgs = ch_fetch.filter_missing_packages(
-        determine_purge_packages())
-    if installed_pkgs:
-        ch_fetch.apt_purge(installed_pkgs, fatal=True)
-        ch_fetch.apt_autoremove(purge=True, fatal=True)
+    remove_old_packages()
 
     disable_policy_rcd()