Don't return a host referral to the service realm

A host referral to the same realm we just looked up the principal in
is useless at best and confusing to the client at worst.  Don't
respond with one in the KDC.

(back ported from commit ee0d5eac353a13a194759b72cb44203fda1bf0fa)

ticket: 7536 (new)
version_fixed: 1.10.4
status: resolved