This is a continuation of issues #3973 and #3974.

Finally, the case where the fail over code needs to do additional lookups
in order to resolve at least the amount of host names requested by the
krb5_kdcinfo_lookahead should be addressed. The caller that initializes
the fail over service (maybe with be_fo_add_service) should provide
a hint with the value of the lookahead option. Then, if a request for
server resolution is triggered, the fail over code would resolve a server
and afterwards check if enough fo_server entries with a valid hostname
in the struct server_common structure. If not, the request would
check if any of the fo_server structures represents a SRV query and
try to resolve the query to receive more host names.