common.sh: Add retry logic to loopback_partscan (backport)

We have continually had issues with mounting and
unmounting loopback partitions via partx. This commit
adds a mechanism to retry as well as fully detach
and reattach using losetup.

BUG=chromium:1011891
TEST=tryjob

Change-Id: I25be8f82cfaa58a59945f64282e0b42d41fbbc7d
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/1898925
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: George Engelbrecht <engeg@google.com>
Commit-Queue: George Engelbrecht <engeg@google.com>
Tested-by: George Engelbrecht <engeg@google.com>
Auto-Submit: George Engelbrecht <engeg@google.com>
1 file changed