This copies the same warnings from the API reference change
I85e7c2677f4d5eccc1e7f349de06960b53ef148d to the CLI help
for the various evacuate/live migrate commands. It also
mentions that if a host is not specified, one is selected
by the scheduler (which is what we really want people doing).
Given blueprint remove-force-flag-from-live-migrate-and-evacuate
we really want to discourage people from using the --force
flag.
Change-Id: I15ef933cc09947e2bb3fb7bf17b15735171a9bec
578b37f994