Remove ThreadPool with async executor (#4154)

* Remove ThreadPool with async executor

* Fix zigbee

* update unittest

* fix remote api

* add pending task to remote

* fix lint

* remove unused import

* remove old stuff for lazy tests

* fix bug and add a exception handler to executor

* change executor handling

* change to wait from gather

* fix unittest

tests/components/camera/test_local_file.py

@@ -14,8 +14,6 @@ from tests.common import assert_setup_component, mock_http_component
 @asyncio.coroutine
 def test_loading_file(hass, test_client):
     """Test that it loads image from disk."""
-    hass.allow_pool = True
-
     @mock.patch('os.path.isfile', mock.Mock(return_value=True))
     @mock.patch('os.access', mock.Mock(return_value=True))
     def setup_platform():