Don't cache referral and alternate TGT replies

Don't cache referral and alternate TGT replies

During a TGS request, if we get a TGT response that we didn't directly
ask for (a referral TGT or an alternate TGT), don't cache it.  It
would have limited value in the cache as similar operations won't look
for that TGT.  If the overall TGS operation fails and is repeated, we
could wind up caching the same entry multiple times, which doesn't
work well with our current ccache implementations.

ticket: 8579