Allow empty settings to disable start/stop program

Partial fix to allow openstack-monitoring take no action and monitor
only for rabbitmq.

Issues rcbops/chef-cookbooks#860 and rcbops/chef-cookbooks#909

(cherry picked from commit 3fcbfa5a5f9234a77f2cc1c64ac9664c54a920b7)
Merge pull request #42 from claco/v4.2.3rc

Merged automatically by jenkins after successful build test