Make sure logs are archived after broctl kills Bro

During a "broctl stop", if a Bro node doesn't terminate within
a set time interval (defined by the broctl option StopTimeout),
then broctl kills that Bro node with SIGKILL.  In this scenario,
it is unlikely that Bro would have had a chance to execute
"archive-log", so any unarchived log files would be removed as part
of the normal cleanup (via "post-terminate") that happens when
"broctl stop" is issued.

Fixed by adding a new command-line option to "post-terminate"
indicating that the Bro node was killed and "archive-log"
needs to be run in order to archive any remaining log files.

Addresses BIT-1126
Update a test to verify logs get archived when bro is killed
Merge remote-tracking branch 'origin/topic/dnthayer/ticket1126'

* origin/topic/dnthayer/ticket1126:
  Update a test to verify logs get archived when bro is killed
  Make sure logs are archived after broctl kills Bro

BIT-1126 #merged