Test multi-value host referral variables

host_based_services and no_host_referral are allowed to have multiple
relations in each place they appear, so alter a couple of the test
cases to exercise that.
Simplify KDC host referral code

Remove some unnecessary optimizations to reduce code complexity.  Get
rid of krb5_match_config_pattern in favor of a simpler helper function
in do_tgs_req_c.  Get rid of KRB5_CONF_ASTERISK and just use "*"
instead.  Use a helper function to combine [kdcdefaults] and realm
subsection values of variables, and don't bother adding leading and
trailing spaces.  Consistently use the names "hostbased" and
"no_referral" to refer to variable values (with a "realm_" prefix for
structures which currently use it).