Limit HAProxy exec check to primary controller

HAProxy IP is controlled by Pacemaker/Corosync. Exec fails on all Slave controllers.
This patch limits exec check to primary controller only.

Change-Id: Ic8daace980f2cb01feeb1f8006c9ca22d4a6a8f2
Closes-Bug: 1329780
Related-Bug: 1321662
Merge "Limit HAProxy exec check to primary controller"