This patch adds a new optional 'job-id' parameter to 'blockdev-backup'
and 'drive-backup', allowing the user to specify the ID of the block
job to be created.

The HMP 'drive_backup' command remains unchanged.
Signed-off-by: NAlberto Garcia <berto@igalia.com>
Reviewed-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NMax Reitz <mreitz@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>