Fix MongoDB successful connection logging.
Fix MongoDB successful connection logging.

Since pymongo 3.0, client.connect() method is not blocking anymore and
always successfuly returns. Connection is established lazily when a
first query / command is issued.

This means we incorrectly always logged "Successfully connected to
database" when a connection was not established yet and when subsequent
queries failed.

StackStorm/st2,nzlosh/st2,nzlosh/st2,StackStorm/st2,Plexxi/st2,StackStorm/st2,nzlosh/st2,nzlosh/st2,StackStorm/st2,Plexxi/st2,Plexxi/st2,Plexxi/st2