When nailgun-agent starts before device mapper
assembles multipath devices it reports physical disks
that are used for multipath devices as usual disks.
This patch does the following
* filter out devices that are DM_MULTIPATH_DEVICE_PATH = 1
* run 'udevadm settle' before scanning multipath devices
* delays scanning multipath devices until building block device info
(cherry picked from commit 8fbc4d6405)