Handle loop device partitions.

Loop devices can have partitions on them which follow naming conventions
similar to mmcblk devices (/dev/loop2p4).

BUG=chromium:349045
TEST=Unittests.

Change-Id: I653ae88eae69e638185a01e736900f0b695ce992
Reviewed-on: https://chromium-review.googlesource.com/190892
Reviewed-by: Alex Deymo <deymo@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>
Commit-Queue: Don Garrett <dgarrett@chromium.org>
Tested-by: Don Garrett <dgarrett@chromium.org>
3 files changed