BZ #1128361 - Correctly check for openstack-heat-engine service

https://bugzilla.redhat.com/show_bug.cgi?id=1128361

Use Quickstack::Pacemaker::Resource::Service instead of Exec to check
that heat engine is up
Merge pull request #352 from bcrochet/bz/1128361

BZ #1128361 - Correctly check for openstack-heat-engine service