Fix bugs in recent locate_kdc.c change

Fix bugs in recent locate_kdc.c change

The most recent change to locate_srv_conf_1() introduced a possible
double-free bug (detected by Coverity), and also broke MS-KKDCP
support.  Separate the three uses of the "host" variable: the C string
copy of the realm name (now "realmstr"), the pointer to the hostname
or hostname:port specification in the profile values array (now
"hostspec"), and the hostname result of k5_parse_host_string() (still
"host").  Pass the correct pointer to k5_parse_host_string() if the
profile value is a URI.