packaging: Make vdms_reg bridge configurable

Added -with-reg-bridge-name= option to configure script which defaults
to ovirtmgmt.

Change-Id: I805a5b14d0dce6eca1c315f0eed490952311f70c
Signed-off-by: Dima Kuznetsov <dkuznets@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/30818
Reviewed-by: Dan Kenigsberg <danken@redhat.com>