Remove use of IsolatedAsyncioTestCase.

It's not available in all versions of Python we support.

tests/contacts/test_contact_tcp.py

@@ -1,16 +1,15 @@
 import logging
 import socket
 from unittest import mock
-from unittest import IsolatedAsyncioTestCase
 
 from app.contacts.contact_tcp import TcpSessionHandler
 
 logger = logging.getLogger(__name__)
 
 
-class TestTcpSessionHandler(IsolatedAsyncioTestCase):
+class TestTcpSessionHandler:
 
-    async def test_refresh_with_socket_errors(self):
+    def test_refresh_with_socket_errors(self, loop):
         handler = TcpSessionHandler(services=None, log=logger)
 
         session_with_socket_error = mock.Mock()
@@ -22,17 +21,17 @@ async def test_refresh_with_socket_errors(self):
             mock.Mock()
         ]
 
-        await handler.refresh()
+        loop.run_until_complete(handler.refresh())
         assert len(handler.sessions) == 1
         assert all(x is not session_with_socket_error for x in handler.sessions)
 
-    async def test_refresh_without_socket_errors(self):
+    def test_refresh_without_socket_errors(self, loop):
         handler = TcpSessionHandler(services=None, log=logger)
         handler.sessions = [
             mock.Mock(),
             mock.Mock(),
             mock.Mock()
         ]
 
-        await handler.refresh()
+        loop.run_until_complete(handler.refresh())
         assert len(handler.sessions) == 3