name_lookup() now returns all results given by getnameinfo(). When searching
for a server, finding one matching address in the lookup-results is enough for
a match.
Also, added a test for name_lookup(). The test is minimal on its own, as hardcoded
test cases are not generally valid.
When matching hostnames between MaxScale server configuration and the
SHOW SLAVE STATUS-output, use DNS-resolution if a simple string comparison
doesn't find an answer. Results of the resolution are saved to avoid
repeating the operation for the same address.
