vdsm-tool: use geteuid() instead of getuid() for root check.

This is expected to have no consequence. checking for effective user id
is more accurate for permissions check.

Change-Id: I0a54af5737cf47e3f5e8ab62339bddd978ceddb9
Signed-off-by: Mooli Tayer <mtayer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/31317
Reviewed-by: Dima Kuznetsov <dkuznets@redhat.com>
Reviewed-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>