Create a container class and a flag for enable it from command line

Ref #417

gns3server/controller/__init__.py

@@ -0,0 +1,41 @@
+#!/usr/bin/env python
+#
+# Copyright (C) 2016 GNS3 Technologies Inc.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# 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 General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+
+from ..config import Config
+
+
+class Controller:
+    """The controller manage multiple gns3 servers"""
+
+    def isEnabled(self):
+        """
+        :returns: True if current instance is the controller
+        of our GNS3 infrastructure.
+        """
+        return Config.instance().get_section_config("Server").getboolean("controller")
+
+    @staticmethod
+    def instance():
+        """
+        Singleton to return only on instance of Controller.
+        :returns: instance of Controller
+        """
+
+        if not hasattr(Controller, '_instance') or Controller._instance is None:
+            Controller._instance = Controller()
+        return Controller._instance