Tunnel mesh was not fully created.

Tunnel mesh was not fully created.

There is a timing issue between SB and NB event while
creating bridge. When we are trying to add bridge to
ovsdb from SB, NB is trying to add port for same bridge.
during which NB will check DS/cache for bridge entry,
which will be empty as SB is trying to add it in ovsdb
at the same time. So we are adding eventcallback to
synchronize both events.

Change-Id: I7c33f41591de27972742df14ae913daae7f6889f
Signed-off-by: Nidhi <nidhi.adhvaryu@ericsson.com>