klog.krb5: enforce DES for rxkad

klog.krb5: enforce DES for rxkad

0. Always request a TGT regardless of the state of
   writeTicketFile.

1. request des-cbc-crc when requesting a ticket for an
   rxkad service principal

2. check the returned key length to ensure that it matches
   the permitted length of an rxkad key.  If not, generate
   an error instead of overwriting memory and continuing.

FIXES 130278

Reviewed-on: http://gerrit.openafs.org/5619
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Tested-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
(cherry picked from commit 3a9a5783cd1fd73902655f0876e2069b42688c94)

Change-Id: Ia162cb9fc1d67a38cde26e52b9077f5634a62c84
Reviewed-on: http://gerrit.openafs.org/6087
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>