Fixed vpnaas agent for RedHat systems

The package vpnaas package was not installed by default for RedHat
systems, and the service had the incorrect name. This patch
installs the package and sets the correct service name.

Backport to stable/havana

Change-Id: Id54dfbcb918d7d9ba110eb238858162c5cc0380e
(cherry picked from commit f3f723277d5c73d46890ce6872fbeeb11a5c2797)
Merge "Fixed vpnaas agent for RedHat systems" into stable/havana