Added a hasMasterConnection() method to LoadBalancer

* Made wfWaitForSlaves() use it instead of using isOpen() incorrectly.
  The index for the master is 0, not DB_MASTER. This fixes 2979f0b6.

Change-Id: I48e5c7f10d8fe6b8bf6e830282352e3238b5d3ae
Merge "Added a hasMasterConnection() method to LoadBalancer"