execCmd with sudo=root raise require tty fault when running as root

As default sudo request requires tty, although we define notty for user
vdsm, if we'll try to call sudo command as another use (also root) we
will be blocked by the "sorry you must have tty" to execute sudo
command. To avoid that, this patch ignores sudo=True parameter in
execCmd while running as root.

Change-Id: Iba4175061fe9500ce912a319f63cde9a8b62ab63
Signed-off-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/23721
Reviewed-by: Alon Bar-Lev <alonbl@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>