multipath: add udev sync support.

multipath: add udev sync support.

device-mapper in now able to synchronize operations through udev.  This patch
allows multipath and kpartx to make use of this feature. If kpartx is run with
"-s", it waits for the partitions to be created before returning. Multipath
will now always wait for the devices to be created before returning.

This feature requires dm_task_set_cookie() which was finalized in device-mapper
version 1.2.38

Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>