Introduce a new QMP command 'blockdev-change-medium' which is intended
to replace the 'change' command for block devices. The existing function
qmp_change_blockdev() is accordingly renamed to
qmp_blockdev_change_medium().
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>