Windows: Mount points are always directories

Windows: Mount points are always directories

Set the directory file attribute for all mount points
since a mount point target is always represented as
a directory.

Change-Id: I57a8e44d1382093311e8263c18d55f22f2f745ea
Reviewed-on: http://gerrit.openafs.org/5784
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Peter Scott <pscott.kd@gmail.com>
Tested-by: Peter Scott <pscott.kd@gmail.com>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>