Windows: FILE_READ_ONLY_VOLUME not FILE_DEVICE_READ_ONLY

Instead of stating that the AFS device is read only; report
that the volume in question is read only using the FILE_READ_ONLY_VOLUME
file system characteristic.

Change-Id: I0b172f8a984802a3cefdea84436c9ed44f34d7f1
Reviewed-on: http://gerrit.openafs.org/8975
Reviewed-by: Rod Widdowson <rdw@steadingsoftware.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>
Windows: .readonly space reporting

.readonly volumes can be stored on multiple partitions which each
have a different size and free space available.  To ensure consistency
regardless of which partition the .readonly is accessed from and
because .readonly volume sizes cannot change, report the allocation
size of the volume as the partition size.  Continue to report that
volume has zero free sectors because the volume cannot be written to.

Change-Id: Ib57b1175da048344af615b9350d72d9eb3ffe97d
Reviewed-on: http://gerrit.openafs.org/8976
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>