Unset DB init flag on shared-db relation removal

The keystone charm sets db-initialised to true after initializing the
database the first time.  However, if the database application is
removed, this flag is not unset.

This results in breakage on attempts to re-add a shared-db relation
with a new database application, as the charm will not attempt to
re-initialize the database prior to doing DB operations.

This fix simply ensures that we unset this flag prior to finalizing
removal of the shared-db relation.

Change-Id: I78ae12fda05ce006939b2d90a3d738bacb815915
Closes-Bug: #1797229

hooks/keystone_hooks.py

@@ -50,6 +50,7 @@ from charmhelpers.core.hookenv import (
     open_port,
     is_leader,
     relation_id,
+    leader_set,
 )
 
 from charmhelpers.core.host import (
@@ -393,6 +394,13 @@ def db_changed():
         update_all_identity_relation_units()
 
 
+@hooks.hook('shared-db-relation-departed',
+            'shared-db-relation-broken')
+def db_departed_or_broken():
+    if is_leader():
+        leader_set({'db-initialised': None})
+
+
 @hooks.hook('identity-service-relation-changed')
 @restart_on_change(restart_map(), restart_functions=restart_function_map())
 def identity_changed(relation_id=None, remote_unit=None):

hooks/shared-db-relation-broken

@@ -0,0 +1 @@
+keystone_hooks.py

hooks/shared-db-relation-departed

@@ -0,0 +1 @@
+keystone_hooks.py