Adds Warning when NetworkManager is active on hosts

Change-Id: I1e4e20ae112936fab880b50d45686c4989ae7fbd
Fixes: rhbz#1117115
Signed-off-by: Gael Chamoulaud <gchamoul@redhat.com>
(cherry picked from commit 2faa9a2cb616615f189a7ed6a7eade9a9f12c0e6)
Merge "Adds Warning when NetworkManager is active on hosts" into icehouse