Handle all exceptions in log-pusher.py.

* modules/openstack_project/files/logstash/log-pusher.py: Catch and
log all exceptions that make it to the top of our poll loops. Allows
for greater debugging of the script.

Change-Id: I4f8bb2ea1629ee98f5e70c978a299c889a22a939
Reviewed-on: https://review.openstack.org/27876
Reviewed-by: James E. Blair <corvus@inaugust.com>
Approved: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Tested-by: Jenkins