Use mongodb charm in k8s installer

- Update JUJU_AGENT_VERSION to 2.8.6
- Use mongodb charm and update needed osm pod specs to point at it

Change-Id: I75734a19aaa5b3b7a8913591ee86a8e1b82b29cd
Signed-off-by: David Garcia <david.garcia@canonical.com>
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>
diff --git a/installers/docker/osm_pods/mon.yaml b/installers/docker/osm_pods/mon.yaml
index 31808aa..490889f 100644
--- a/installers/docker/osm_pods/mon.yaml
+++ b/installers/docker/osm_pods/mon.yaml
@@ -59,6 +59,8 @@
           value: kafka
         - name: OSMMON_MESSAGE_PORT
           value: "9092"
+        - name: OSMMON_DATABASE_URI
+          value: mongodb://mongodb-k8s:27017/?replicaSet=rs0
         envFrom:
         - secretRef:
            name: mon-secret