Bug 928752: Run threaddump/system-messages only on primary cart

Fix a regression whereby threaddump and system-messages actions were being
sent to non-primary cartridges.

Resolve https://bugzilla.redhat.com/show_bug.cgi?id=928752.
Merge pull request #1863 from ironcladlou/stage/bz/928752

Merged by openshift-bot