This option duplicates the more generic
[compute-feature-enabled]/block_migration_for_live_migration now that
MIN_LIBVIRT_VERSION is >= 1.2.17 on all branches from stable/rocky. We
can deprecate this now ahead of removal once stable/pike and
stable/queens are no longer supported.
Change-Id: I8d8ae5ebf8e1d383f184527815f0a0c0ba9a343d