Allow Lemur "start" to use the global config. (#596)

* allowing our runserver to use the config specified by -c

* Maintaining config for gunicorn

lemur/common/managers.py

@@ -60,11 +60,14 @@ class InstanceManager(object):
                     results.append(cls())
                 else:
                     results.append(cls)
+
             except InvalidConfiguration as e:
                 current_app.logger.warning("Plugin '{0}' may not work correctly. {1}".format(class_name, e))
+
             except Exception as e:
                 current_app.logger.exception("Unable to import {0}. Reason: {1}".format(cls_path, e))
                 continue
+
         self.cache = results
 
         return results