block: rescan partitions on invalidated devices on -ENOMEDIA too

__blkdev_get() doesn't rescan partitions if disk->fops->open() fails,
which leads to ghost partition devices lingering after medimum removal
is known to both the kernel and userland.  The behavior also creates a
subtle inconsistency where O_NONBLOCK open, which doesn't fail even if
there's no medium, clears the ghots partitions, which is exploited to
work around the problem from userland.

Fix it by updating __blkdev_get() to issue partition rescan after
-ENOMEDIA too.

This was reported in the following bz.

 https://bugzilla.kernel.org/show_bug.cgi?id=13029

Note for stable: 2.6.38 and later only

Cc: [email protected]
Signed-off-by: Tejun Heo <[email protected]>
Reported-by: David Zeuthen <[email protected]>
Reported-by: Martin Pitt <[email protected]>
Reported-by: Kay Sievers <[email protected]>
Tested-by: Kay Sievers <[email protected]>
Cc: Alan Cox <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>

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