ThreadPool timeout when checking tserver stats is confusing

If it takes longer than the configured time to gather information from all the tablet servers, the thread pool stops and processing continues with whatever has been collected. Code is https://github.com/apache/accumulo/blob/1.8/server/master/src/main/java/org/apache/accumulo/master/Master.java#L1120, default timeout is 6s. Does not appear to be an issue prior to 1.8.

Best case, this was really confusing. The monitor page would have 30 tservers, then 5 tservers. Didn't really see any other negative effects, no migrations and no balancing appeared to be affected. Worse case though, I missed something and the master is making decisions based on incomplete information.

dlmarion@comcast.net please add more info if needed.