CBST-19: improve process/thread management

1) use super.terminate() to kill proc
started noticing lots of consumer processes while running
test with 10 phases.  this is because the processes accumulated
without calling terminate() in the parent
2) catch NetworkError exception, these do not merrit restarting thread
3) flush hotset only when client thread dies/stopped

Change-Id: I75644876828a1f1b345df418ee0b7b561ae9a860
Reviewed-on: http://review.couchbase.org/30548
Reviewed-by: Ketaki Gangal <ketakigangal@gmail.com>
Tested-by: Tommie McAfee <tommie@couchbase.com>