vdsm-reg-setup: add import errno

During vdsm-reg service start it can throw an error about errno.EEXIST
doesn't exist. This patch adds the import errno.

Change-Id: I3d0836d060d2882b57d38e7299c3302312835f82
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/26994
Reviewed-by: Dan Kenigsberg <danken@redhat.com>