vdsm: packages: disable NetworkManager service by default

NetworkManager causes timing issues with network service and vdsm.

See rhbz#879180.

Antoni Segura Puimedon:
> I was confirming the state of affairs with NM guys.
> They said that:
> "no, it [the fix in https://bugzilla.redhat.com/show_bug.cgi?id=879180 ]
> is not in F19. But there are changes in master (will go to F20, RHEL7),
> one of them being the thing that NM won't monitor ifcfg file changes
> (but will read the changed files only on explicit request)"
>
> So this change is necessary until then.

Change-Id: Ie309c2939f44b3bc2f44eb9e892cbd118651a41a
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>