Add discovery notify support and mysensors notify (#5219)

* Add mysensors notify platform

* Make add_devices optional in platform callback function.
* Use new argument structure for all existing mysensors platforms.
* Add notify platform.
* Update mysensors gateway.

* Refactor notify setup

* Enable discovery of notify platforms.
* Update and add tests for notify component and some platforms.
* Continue setup of notify platforms if a platform fails setup.
* Remove notify tests that check platform config. These tests are not
  needed when config validation is used.
* Add config validation to APNS notify platform.
* Use discovery to set up mysensors notify platform.

* Add discovery_info to get_service and update tests

* Add discovery_info as keyword argument to the get_service function
  signature and update all notify platforms.
* Update existing notify tests to check config validation using test
  helper.
* Add removed tests back in that checked config in apns, command_line
  and file platforms, but use config validation test helper to verify
  config.
* Add a test for notify file to increase coverage.
* Fix some PEP issues.

* Fix comments and use more constants

* Move apns notify service under notify domain

tests/components/notify/test_command_line.py

@@ -6,7 +6,7 @@ from unittest.mock import patch
 
 from homeassistant.bootstrap import setup_component
 import homeassistant.components.notify as notify
-from tests.common import get_test_home_assistant
+from tests.common import assert_setup_component, get_test_home_assistant
 
 
 class TestCommandLine(unittest.TestCase):
@@ -22,34 +22,41 @@ class TestCommandLine(unittest.TestCase):
 
     def test_setup(self):
         """Test setup."""
-        assert setup_component(self.hass, 'notify', {
-            'notify': {
-                'name': 'test',
-                'platform': 'command_line',
-                'command': 'echo $(cat); exit 1',
-            }})
+        with assert_setup_component(1) as handle_config:
+            assert setup_component(self.hass, 'notify', {
+                'notify': {
+                    'name': 'test',
+                    'platform': 'command_line',
+                    'command': 'echo $(cat); exit 1', }
+            })
+        assert handle_config[notify.DOMAIN]
 
     def test_bad_config(self):
         """Test set up the platform with bad/missing configuration."""
-        self.assertFalse(setup_component(self.hass, notify.DOMAIN, {
-            'notify': {
+        config = {
+            notify.DOMAIN: {
                 'name': 'test',
-                'platform': 'bad_platform',
+                'platform': 'command_line',
             }
-        }))
+        }
+        with assert_setup_component(0) as handle_config:
+            assert setup_component(self.hass, notify.DOMAIN, config)
+        assert not handle_config[notify.DOMAIN]
 
     def test_command_line_output(self):
         """Test the command line output."""
         with tempfile.TemporaryDirectory() as tempdirname:
             filename = os.path.join(tempdirname, 'message.txt')
             message = 'one, two, testing, testing'
-            self.assertTrue(setup_component(self.hass, notify.DOMAIN, {
-                'notify': {
-                    'name': 'test',
-                    'platform': 'command_line',
-                    'command': 'echo $(cat) > {}'.format(filename)
-                }
-            }))
+            with assert_setup_component(1) as handle_config:
+                self.assertTrue(setup_component(self.hass, notify.DOMAIN, {
+                    'notify': {
+                        'name': 'test',
+                        'platform': 'command_line',
+                        'command': 'echo $(cat) > {}'.format(filename)
+                    }
+                }))
+            assert handle_config[notify.DOMAIN]
 
             self.assertTrue(
                 self.hass.services.call('notify', 'test', {'message': message},
@@ -63,13 +70,15 @@ class TestCommandLine(unittest.TestCase):
     @patch('homeassistant.components.notify.command_line._LOGGER.error')
     def test_error_for_none_zero_exit_code(self, mock_error):
         """Test if an error is logged for non zero exit codes."""
-        self.assertTrue(setup_component(self.hass, notify.DOMAIN, {
-            'notify': {
-                'name': 'test',
-                'platform': 'command_line',
-                'command': 'echo $(cat); exit 1'
-            }
-        }))
+        with assert_setup_component(1) as handle_config:
+            self.assertTrue(setup_component(self.hass, notify.DOMAIN, {
+                'notify': {
+                    'name': 'test',
+                    'platform': 'command_line',
+                    'command': 'echo $(cat); exit 1'
+                }
+            }))
+        assert handle_config[notify.DOMAIN]
 
         self.assertTrue(
             self.hass.services.call('notify', 'test', {'message': 'error'},