dirpath: update keytab strings in windows

this was missed in the pullup from 33eecea7db14d06c59e1081b970d4caf0af773ca

Change-Id: Iee734bf06af4152ead5cfcf33bbbcafc39812c5a
Reviewed-on: http://gerrit.openafs.org/10109
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>