[v8r5] Fix BKWatchAgent
_getFiles doesn't need @gSynchro which is a disaster in case of timeout: the BookkeepingClient is now creating a new connection each time a method is invoked, therefore it is thread-safe. The @gSynchro was slowing down considerably the agent in case the BK was taking long to return (up to 10 minutes timeout): some threads were taking 10, 20, 30, 40 minutes before executing their query