Define ACTIVE_PROVIDERS in default config
Define ACTIVE_PROVIDERS in default config

The configuration item ACTIVE_PROVIDERS must be initialized

Workaround for this error:
2015-12-30 13:58:48,073 ERROR: Internal Error [in /www/lemur/local/lib/python2.7/site-packages/flask_restful/__init__.py:299]
Traceback (most recent call last):
  File "/www/lemur/local/lib/python2.7/site-packages/flask/app.py", line 1475, in full_dispatch_request
    rv = self.dispatch_request()
  File "/www/lemur/local/lib/python2.7/site-packages/flask/app.py", line 1461, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/www/lemur/local/lib/python2.7/site-packages/flask_restful/__init__.py", line 462, in wrapper
    resp = resource(*args, **kwargs)
  File "/www/lemur/local/lib/python2.7/site-packages/flask/views.py", line 84, in view
    return self.dispatch_request(*args, **kwargs)
  File "/www/lemur/local/lib/python2.7/site-packages/flask_restful/__init__.py", line 572, in dispatch_request
    resp = meth(*args, **kwargs)
  File "/www/lemur/lemur/auth/views.py", line 276, in get
    for provider in current_app.config.get("ACTIVE_PROVIDERS"):
TypeError: 'NoneType' object is not iterable
Netflix/lemur,nevins-b/lemur,kevgliss/lemur,Netflix/lemur,Netflix/lemur,nevins-b/lemur,nevins-b/lemur,kevgliss/lemur,Netflix/lemur,kevgliss/lemur