'join_host_strings() should use square brackets only for IPv6 and if port is given'

def test_ipv6_host_strings_join(self):

    eq_(join_host_strings('user', '2001:DB8::1'), 'user@2001:DB8::1')
    eq_(join_host_strings('user', '2001:DB8::1', '1222'), 'user@[2001:DB8::1]:1222')
    eq_(join_host_strings('user', '192.168.0.0', '1222'), 'user@192.168.0.0:1222')
