auth: Force correct evenness on rxkad tokens

auth: Force correct evenness on rxkad tokens

Rxkad tokens historically have forced odd lifetimes when the given
viceid is actually an AFS ID, and even lifetimes when it is not. Force
this when the new token-handling functions are used (so the viceid is
correctly interpreted by users of the old token format), by creating
rxkad tokens with token_importRxkadViceId.

Slightly reworked by Simon Wilkinson to provide a generic token
destructor function.

Change-Id: I9f6aa518b8ae51a3772b69a0722a28bff6b47128
Reviewed-on: http://gerrit.openafs.org/4481
Tested-by: Simon Wilkinson <sxw@inf.ed.ac.uk>
Reviewed-by: Derrick Brashear <shadow@dementix.org>