Deal with py2-py3 payload switch during upgrade-charm

Switch to using the default upgrade-charm handler as provided
by charms.openstack and associated layers.

This ensures that the payload execution switch from py2->py3
at OpenStack Rocky is implemented during the charm upgrade
process.

Change-Id: I8dc19abe813fb78f16cfb0abdbb40cf2ee9a4e6e
Closes-Bug: 1803451

.gitignore

@@ -3,5 +3,6 @@ layers
 .tox
 interfaces
 .testrepository
+.stestr
 *__pycache__*
 *.pyc

src/lib/charm/openstack/aodh.py

@@ -30,7 +30,10 @@ AODH_API_SYSTEMD_CONF = (
 AODH_WSGI_CONF = '/etc/apache2/sites-available/aodh-api.conf'
 
 
-charms_openstack.charm.use_defaults('charm.default-select-release')
+charms_openstack.charm.use_defaults(
+    'charm.default-select-release',
+    'upgrade-charm'
+)
 
 
 class AodhAdapters(charms_openstack.adapters.OpenStackAPIRelationAdapters):

src/reactive/aodh_handlers.py

@@ -99,11 +99,6 @@ def cluster_connected(hacluster):
     aodh.configure_ha_resources(hacluster)
 
 
-@reactive.hook('upgrade-charm')
-def upgrade_charm():
-    aodh.install()
-
-
 # TODO: drop once charm switches to apache+mod_wsgi
 @reactive.when_file_changed(aodh.AODH_API_SYSTEMD_CONF)
 def systemd_override_changed():