md: add bitmap_abort label in md_run

Now, there are two places need to consider about
the failure of destroy bitmap, so move the common
part between bitmap_abort and abort label.

Reviewed-by: NeilBrown <neilb@suse.com>
Signed-off-by: Guoqing Jiang <gqjiang@suse.com>
Signed-off-by: Song Liu <songliubraving@fb.com>