Bug#254945: b0rks if /target already exists

[Petter Reinholdtsen <pere@hungry.com>]

tags 254945 - patch
thanks

Is this bugreport about partman-auto or autopartkit?  I'm a bit
confused.  I'm not seeing any patch, so I remove that tag for the bug
report.

I know that autopartkit will fail when executed after /target/ is
mounted.  This is both related to the fact that directory creation
will fail, and also to the fact that the kernel caches partition table
info if the disk has been in use.  Not sure how to get around that.
Patches are welcome. :)