volser: Make VolListOneVolume errors consistent

Currently, VolXListOneVolume errors out with ENODEV if any attachment
error occurs with the specified volume. But VolListOneVolume always
returns success if it can find the indicated volume, and any
attachment errors and such are reported in the 'status' field of the
volume info structure.

These two functions do pretty much the same thing; VolXListOneVolume
just provides more info than VolListOneVolume. So make them behave the
same way, and provide more specific information, whether or not
somebody ran 'vos examine' or 'vos examine -extended'.

The 'vos' binary has always handled errors in the 'status' volume info
structure for both "extended" and non-"extended" queries. This
difference appears to just have been a mistake from OpenAFS 1.0.

Change-Id: Iab16ef6a25487d492fdb046db93973a1e64ca70a
Reviewed-on: http://gerrit.openafs.org/9680
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>