Create missing root directory when ORPH_ATTACH

Create missing root directory when ORPH_ATTACH

When we are salvaging with ORPH_ATTACH, orphans are normally attached to
a volume's root directory. If the volume is missing a root directory,
however, nothing is attached, and the volume can appear empty or
unusable.

So, to make it possible to get a useful volume out of a volume that lost
(only) its root directory, create a new root dir, and attach orphans to
that root.

FIXES 94658

Change-Id: I946a60485b5793952707f44ac369ee243e8dc076
Reviewed-on: http://gerrit.openafs.org/1235
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>