auth: Implement __str__ on plugin base class

This way some error messages will look nicer, since they are based on the
__str__ of the plugin instance. Using the plugin_id will give the user (and us
in the support case) the exact pointer to the affected plugins.

rhodecode/authentication/base.py

@@ -107,6 +107,9 @@ class RhodeCodeAuthPluginBase(object):
     def __init__(self, plugin_id):
         self._plugin_id = plugin_id
 
+    def __str__(self):
+        return self.get_id()
+
     def _get_setting_full_name(self, name):
         """
         Return the full setting name used for storing values in the database.

rhodecode/authentication/tests/test_auth_plugin_base.py

@@ -0,0 +1,28 @@
+# Copyright (C) 2016  RhodeCode GmbH
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License, version 3
+# (only), as published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+# This program is dual-licensed. If you wish to learn more about the
+# RhodeCode Enterprise Edition, including its added features, Support services,
+# and proprietary license terms, please see https://rhodecode.com/licenses/
+
+"""
+Checks around the API of the class RhodeCodeAuthPluginBase.
+"""
+
+from rhodecode.authentication.base import RhodeCodeAuthPluginBase
+
+
+def test_str_returns_plugin_id():
+    plugin = RhodeCodeAuthPluginBase(plugin_id='stub_plugin_id')
+    assert str(plugin) == 'stub_plugin_id'