Adding MON relation to Keystone for charmed OSM

Change-Id: Icc81251002736a4e25579f42500a5a8f6b3fe74a
Signed-off-by: calvinosanc1 <guillermo.calvino@canonical.com>
diff --git a/installers/charm/mon/metadata.yaml b/installers/charm/mon/metadata.yaml
index 05aa547..663315e 100644
--- a/installers/charm/mon/metadata.yaml
+++ b/installers/charm/mon/metadata.yaml
@@ -45,3 +45,5 @@
     interface: mongodb
   prometheus:
     interface: prometheus
+  keystone:
+    interface: keystone