Change regional endpoint doname name

Author: rayluo

msal/application.py

@@ -371,7 +371,7 @@ def _get_regional_authority(self, central_authority):
             self._region_configured if is_region_specified else self._region_detected)
         if region_to_use:
             logger.info('Region to be used: {}'.format(repr(region_to_use)))
-            regional_host = ("{}.login.microsoft.com".format(region_to_use)
+            regional_host = ("{}.r.login.microsoftonline.com".format(region_to_use)
                 if central_authority.instance in (
                     # The list came from https://github.com/AzureAD/microsoft-authentication-library-for-python/pull/358/files#r629400328
                     "login.microsoftonline.com",

tests/test_e2e.py

@@ -798,7 +798,7 @@ def test_acquire_token_for_client_should_hit_regional_endpoint(self):
                 status_code=400, text='{"error": "mock"}')) as mocked_method:
             self.app.acquire_token_for_client(scopes)
             mocked_method.assert_called_with(
-                'https://westus.login.microsoft.com/{}/oauth2/v2.0/token'.format(
+                'https://westus.r.login.microsoftonline.com/{}/oauth2/v2.0/token'.format(
                     self.app.authority.tenant),
                 params=ANY, data=ANY, headers=ANY)
         result = self.app.acquire_token_for_client(