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.