Removed unnecessary hacks

In Havana release there was necessary to install plugin specific packages
for ML2 because module had not implement it. This is not true for Icehouse
release so hacks have to be removed.

Removed also enable_security_group hack which breaks recent version
of Neutron server.

Change-Id: I35896166bfe4de2c9e49ba59579063fc0b8c666d
Fixes: rhbz#1096510