Add USB control commands to CrostiniManager

This CL allows users of CrostiniManager to add, remove, and list USB
devices attached to a vm. This will ultimately allow USB devices to be
shared with Crostini using the UI.

Bug: 891381
Change-Id: Id81ca37348df5b57c69a76d7f6123cdfac6ec685
Reviewed-on: https://chromium-review.googlesource.com/c/1350417
Commit-Queue: Fergus Dall <sidereal@google.com>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Nicholas Verne <nverne@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#620630}
16 files changed