Remount external device even if formatting fails

Transient issues may cause formatting to fail, so remount the device to
let the user see what happened to the device, and also try format it
again.

Bug: 965806
Change-Id: I4e95f050dd4d48fbe11527be000cfa4c34b22d0d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1624005
Reviewed-by: Anand Mistry <amistry@chromium.org>
Commit-Queue: Austin Tankiang <austinct@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662499}
2 files changed