Fix print_token_and_key

So, it turns out that rxgk_key == krb5_keyblock* == void* != struct rx_opaque*
But the void* typedef prevents the compiler from warning when the
types are blatantly misused to pass into print_token.
The first use of print_token_and_key was in ClientAuthRXGK, so
we didn't notice until now.

Change-Id: If4a7c40649990428a2e3ab7a45294e98787282b5