Fix Warning when NetworkManager is active on hosts

The warning was just displayed in case of multinode installation, and not for
an Allinone installation !

Change-Id: I69105eb5533d7d2f099d51e743f0b9d95a15227d
Fixes: rhbz#1130589
Fixes: rhbz#1117115
Signed-off-by: Gael Chamoulaud <gchamoul@redhat.com>