Bug 31345: Add ability to exit process_message_queue.pl early if any plugin before_se...

Bug 31345: Add ability to exit process_message_queue.pl early if any plugin before_send_messages hook fails

Sometimes it would be better for process_message_queue.pl to stop if a plugin hook fails rather than continue processing. It would be nice if that was a command line option.

Test Plan:
1) Install any plugin with a before_send_messages hook
2) Modify the plugin, add a 'die;' statement at the start of the
   before_send_messages method of the plugin.
3) Run process_message_queue.pl as usual
4) Note the exit code is 0
5) Run it again with the new -e setting
6) Note the exit code is 1

Signed-off-by: Brendan Lawlor <blawlor@clamsnet.org>
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>