Add test for resolving a host to an address

The IPv6 change in b146d74 made a bunch of tests fail because they could
not connect to 'localhost'. They could not connect because only the
first result from getaddrinfo(3) was used, which happened to be the IPv6
`localhost` address. This commit changes those tests to use '127.0.0.1'
and adds a test that explicitly tests that the client can resolve
'localhost'.