brillo chroot: Add ability to move workspace chroots.

Add "brillo chroot --move" to specify a new location for a workspace's
chroot. Does not remove the old chroot (if it exists), or move it's
contents.

BUG=brillo:613
TEST=lint + unittests

Change-Id: I7f3b5f89c6fa7dcdb888bd3ee155bf82de2ac8b5
Reviewed-on: https://chromium-review.googlesource.com/263297
Reviewed-by: Don Garrett <dgarrett@chromium.org>
Commit-Queue: Don Garrett <dgarrett@chromium.org>
Tested-by: Don Garrett <dgarrett@chromium.org>
4 files changed