Support for mongodb replicaset connection (HA).

Added replicaset field in lcm.cfg file, which is used in
mongodb connection string (osm_common/db_mongo.py).

Change-Id: If5b00e9442ac738bcb081c8be8e5a726cbfe7484
Signed-off-by: Vijay Nag B S <vijaynag.bs@tataelxsi.co.in>