ACCUMULO-2964 Try to avoid the exception before tserver actually starts.
ACCUMULO-3139 Reflect on UNIXProcess to get the pid and use kill instead of pkill.

pkill has the potential to overmatch and SIGSTOP+SIGCONT other tablet
servers on the same node. If it tries to match tservers started by
other users, this will also fail, AFAICT.
Merge branch '1.6.1-SNAPSHOT'
ACCUMULO-3139 Some extra test stabilizations for BalanceAfterCommsFailureIT
Merge branch '1.6.1-SNAPSHOT'