Fix typo in log-pusher.py source path.

* openstack_project/manifests/logstash.pp: Change source path from
puppet://modules/... to puppet:///modules/... so that puppet can find
the script.

Change-Id: I9c41f0b158d9ace9e839e34bcba37698b3a8cd18
Reviewed-on: https://review.openstack.org/26402
Reviewed-by: Monty Taylor <mordred@inaugust.com>
Approved: James E. Blair <corvus@inaugust.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins