losetup: Prevent AUTOCLEAR detach race

losetup: Prevent AUTOCLEAR detach race

Kernel needs some time to delete a device after losetup --detach. If
the losetup --find --nooverlay is called just after losetup --delete,
it can sometimes attempt to recycle the device that is just being
released.  To prevent this race, clear the AUTOCLEAR flag of the
device.

[kzak@redhat.com: - rebase to the new version of the code]

Signed-off-by: Stanislav Brabec <sbrabec@suse.cz>
Signed-off-by: Karel Zak <kzak@redhat.com>