tool: bugfix function called as attribute.

to fix bug, introduced in commit 8f87f21, instead of using
selinux.is_selinux_enabled I suggest using the recently added
utils.get_selinux_enforce_mode().

In both cases the code means to check if selinux != disabled
(permissive | enforcing).

Change-Id: Id7c52e6f409b808c79653e40255cf62743b1fd0c
Signed-off-by: Mooli Tayer <mtayer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/34487
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>