Increase the number of retries for db-lock
Increase the number of retries for db-lock

When we decreased the waiting time of db-lock, the operations are
always failed in heavy load, especially in rally.

Increasing the number of retries can ease the problem and it won't
bring any side-effects.

Change-Id: I97abf0bc5c346999a5b55b87e99f8f42a3531b83
Closes-Bug: #1651620

openstack/dragonflow,openstack/dragonflow,openstack/dragonflow