Expose DeleteLxdContainer command in CrostiniManager

Eventually we will want to expose a way to create and delete LXD
containers in the UI. Currently we only have methods to create
containers. This CL adds a new method to CrostiniManager that tells
cicerone to delete an LXD container.

Bug: 927531
Change-Id: I9c571b0fc76bddc93e279a628f11feba4aa8f2bc
Reviewed-on: https://chromium-review.googlesource.com/c/1451597
Commit-Queue: Fergus Dall <sidereal@google.com>
Reviewed-by: Nicholas Verne <nverne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#631518}
14 files changed