block: qcow2: remove the created file on initialization error

If the qcow initialization fails, we should remove the file if it was
already created, to avoid leaving stale files around.

We already do this for luks raw images.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-Id: <20201217170904.946013-4-mlevitsk@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>