There is an optional flag that can be passed in to a
volume migration to tell Cinder to 'lock' a volume so
no other process can abort the migration. This is
reflected correctly with the --lock-volume argument
flag to `openstack volume migrate`, but there is
another --unlock-volume flag that is shown in the help
text for this command that does not do anything and is
not used anywhere.
Since there is no action to "unlock" a volume, this
just causes confusion - including for Cinder developers
that know this API. To avoid confusion, this invalid
flag should just be removed from the command.
Change-Id: I5f111ed58803a1bf5d34e828341d735099247108