Do not rely on when_file_change for systemd reload

Systemd was not relying being reloaded when the definition
file for aodh-api changed. The reload was supposed to be
triggered by the when_file_changed decorator. However,
there are a number of issues with when_file_changed decorator (*1,
*2, *3) and the decorator has now been deprecated *4.

This change ensures the reload happens without relying on
the decorator.

*1 https://github.com/juju-solutions/charms.reactive/issues/25
*2 https://github.com/juju-solutions/charms.reactive/issues/44
*3 https://github.com/juju-solutions/charms.reactive/issues/49
*4 https://github.com/juju-solutions/charms.reactive/issues/44#issuecomment-438472843

Closes-Bug: #1850767

Change-Id: I7c528a53a4de8a4a85bf655fc242b0f38fd0754b

src/lib/charm/openstack/aodh.py

@@ -85,7 +85,7 @@ class AodhCharm(charms_openstack.charm.HAOpenStackCharm):
     # file changes
     restart_map = {
         AODH_CONF: services,
-        AODH_API_SYSTEMD_CONF: 'aodh-api',
+        AODH_API_SYSTEMD_CONF: ['aodh-api'],
     }
 
     # Resource when in HA mode
@@ -125,6 +125,23 @@ class AodhCharm(charms_openstack.charm.HAOpenStackCharm):
             ch_host.service_restart('aodh-api')
 
 
+class AodhCharmNewton(AodhCharm):
+    """Newton uses the aodh-api standalone systemd. If the systemd definition
+       changes the a systemctl daemon-reload is needed.
+    """
+    release = 'newton'
+
+    def render_with_interfaces(self, interface_list):
+        if os.path.exists(AODH_API_SYSTEMD_CONF):
+            old_hash = ch_host.file_hash(AODH_API_SYSTEMD_CONF)
+        else:
+            old_hash = ''
+        super(AodhCharmNewton, self).render_with_interfaces(interface_list)
+        new_hash = ch_host.file_hash(AODH_API_SYSTEMD_CONF)
+        if old_hash != new_hash:
+            self.reload_and_restart()
+
+
 class AodhCharmOcata(AodhCharm):
     """From ocata onwards there is no aodh-api service, as this is handled via
     apache2 with a wsgi handler.  Therefore, these specialisations are simple

src/reactive/aodh_handlers.py

@@ -103,9 +103,3 @@ def run_db_migration():
 @reactive.when('ha.connected')
 def cluster_connected(hacluster):
     aodh.configure_ha_resources(hacluster)
-
-
-# TODO: drop once charm switches to apache+mod_wsgi
-@reactive.when_file_changed(aodh.AODH_API_SYSTEMD_CONF)
-def systemd_override_changed():
-    aodh.reload_and_restart()