Try to fix the travis server errors.

src/greentest/greentest.py

@@ -369,6 +369,18 @@ if PY3 and PYPY:
     CI_TIMEOUT = 10
 LOCAL_TIMEOUT = 1
 
+DEFAULT_LOCAL_HOST_ADDR = 'localhost'
+DEFAULT_LOCAL_HOST_ADDR6 = DEFAULT_LOCAL_HOST_ADDR
+
+if RUNNING_ON_TRAVIS:
+    # As of November 2017 (probably Sept or Oct), after a
+    # Travis upgrade, using "localhost" no longer works,
+    # producing 'OSError: [Errno 99] Cannot assign
+    # requested address'. This is apparently something to do with
+    # docker containers. Sigh.
+    DEFAULT_LOCAL_HOST_ADDR = '127.0.0.1'
+    DEFAULT_LOCAL_HOST_ADDR6 = '::1'
+
 class TestCase(TestCaseMetaClass("NewBase", (BaseTestCase,), {})):
     __timeout__ = LOCAL_TIMEOUT if not RUNNING_ON_CI else CI_TIMEOUT
     switch_expected = 'default'

src/greentest/test__server.py

@@ -86,8 +86,11 @@ class TestCase(greentest.TestCase):
 
     def get_server_host_port_family(self):
         server_host = self.server.server_host
-        if not server_host or server_host == '::':
-            server_host = 'localhost'
+        if not server_host:
+            server_host = greentest.DEFAULT_LOCAL_HOST_ADDR
+        elif server_host == '::':
+            server_host = greentest.DEFAULT_LOCAL_HOST_ADDR6
+
         try:
             family = self.server.socket.family
         except AttributeError:

src/greentest/test__socket.py

@@ -267,7 +267,7 @@ class TestTCP(greentest.TestCase):
         # Issue 841
         s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
         s.setblocking(False)
-        ret = s.connect_ex(('localhost', get_port()))
+        ret = s.connect_ex((greentest.DEFAULT_LOCAL_HOST_ADDR, get_port()))
         self.assertIsInstance(ret, errno_types)
         s.close()
 
@@ -283,7 +283,7 @@ class TestTCP(greentest.TestCase):
         s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
         s.setblocking(False)
         with self.assertRaises(OverflowError):
-            s.connect_ex(('localhost', 65539))
+            s.connect_ex((greentest.DEFAULT_LOCAL_HOST_ADDR, 65539))
         s.close()
 
     @unittest.skipUnless(hasattr(socket, 'SOCK_CLOEXEC'),