Comment 1 for bug 1600328

This is the reason:

2016-07-08 14:26:11 [HTTPChannel,6372,127.0.0.1] 500 Error - /MAAS/api/2.0/machines/
        Traceback (most recent call last):
          File "/usr/lib/python3/dist-packages/twisted/web/wsgi.py", line 496, in run
            appIterator = self.application(self.environ, self.startResponse)
          File "/usr/lib/python3/dist-packages/django/core/handlers/wsgi.py", line 189, in __call__
            response = self.get_response(request)
          File "/usr/lib/python3/dist-packages/maasserver/utils/views.py", line 227, in get_response
            response = get_response(request)
          File "/usr/lib/python3/dist-packages/maasserver/utils/views.py", line 216, in get_response
            request, get_resolver(None), sys.exc_info())
        --- <exception caught here> ---
          File "/usr/lib/python3/dist-packages/maasserver/utils/views.py", line 201, in get_response
            return django_get_response(request)
          File "/usr/lib/python3/dist-packages/maasserver/utils/orm.py", line 479, in __exit__
            self.fire()
          File "/usr/lib/python3/dist-packages/provisioningserver/utils/twisted.py", line 205, in wrapper
            return func(*args, **kwargs)
          File "/usr/lib/python3/dist-packages/maasserver/utils/async.py", line 195, in fire
            self._fire_in_reactor(hook).wait(LONGTIME)
          File "/usr/lib/python3/dist-packages/crochet/_eventloop.py", line 231, in wait
            result.raiseException()
          File "/usr/lib/python3/dist-packages/twisted/python/failure.py", line 368, in raiseException
            raise self.value.with_traceback(self.tb)
          File "/usr/lib/python3/dist-packages/twisted/python/threadpool.py", line 246, in inContext
            result = inContext.theWork()
          File "/usr/lib/python3/dist-packages/twisted/python/threadpool.py", line 262, in <lambda>
            inContext.theWork = lambda: context.call(ctx, func, *args, **kw)
          File "/usr/lib/python3/dist-packages/twisted/python/context.py", line 118, in callWithContext
            return self.currentContext().callWithContext(ctx, func, *args, **kw)
          File "/usr/lib/python3/dist-packages/twisted/python/context.py", line 81, in callWithContext
            return func(*args,**kw)
          File "/usr/lib/python3/dist-packages/provisioningserver/utils/twisted.py", line 937, in callInContext
            return func(*args, **kwargs)
          File "/usr/lib/python3/dist-packages/maasserver/models/node.py", line 2822, in _get_bmc_client_connection_info
            self.hostname))
        maasserver.exceptions.PowerProblem: No rack controllers can access the BMC of node: baubas

Since no power parameters are being specified, this happens.