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
Change-Id: I088aede0cf3bd1d16a57e7cdec4e50cab2c19175
Closes-Bug: #1652788
(cherry picked from commit 8fbc4d6405)