new: [mongo] allow upgrading by maintaining compatibility version at current version.

Signed-off-by: Valentin Lab <valentin.lab@kalysto.org>

mongo/hooks/mongo_database-relation-joined

@@ -88,3 +88,19 @@ else
     exit 14
 fi
 
+
+major_version=${version%.*}
+
+## XXXvlab: why don't we do this initialisation in init ?
+cmd="db.adminCommand( { setFeatureCompatibilityVersion: \"${major_version}\" } )"
+debug "${WHITE}running:$NORMAL $cmd"
+
+out=$(ddb < <(echo "use $DBNAME";
+              echo "$cmd"))
+if [[ "$out" == *"\"ok\" : 1"* ]]; then
+    info "Feature Compatibility set to ${major_version}. "
+else
+    err "Failed to set feature compatibieplicaSet initialisation failed:"
+    echo "$out" | prefix "  | " >&2
+    exit 13
+fi