Fix public VIP gateway ping for neutron

We have different network scheme in astute.yaml for neutron. This
patch fixes public gateway calculation for pacemaker "ping"
resource when we use neutron.

Closes-bug: 1373375
Change-Id: Ia49ba52d3eab5dd5733450901e7a84a3448dbd3d
(cherry picked from commit c08179f54be64de410ef0f54a49b3bd28b0f2f3b)
Merge "Fix public VIP gateway ping for neutron" into stable/5.1