Add command to unmount a removable entry list.

When partitions are grouped, the eject button is attached to the removable root label.
Unmounting a removable root means unmounting all child partitions, and using the
drive label in the unmount message.

Bug: 918795
Change-Id: Idd175c8f3d7a814bfe0784cfa52e35b12c36a663
Reviewed-on: https://chromium-review.googlesource.com/c/1454339
Commit-Queue: Alli Murray <alliemurray@google.com>
Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Cr-Commit-Position: refs/heads/master@{#629867}
3 files changed