'Lists all backends for an app.'

def BackendsList(self):

    if self.args:
        self.parser.error('Expected    no    arguments.')
    appyaml = self._ParseAppInfoFromYaml(self.basepath)
    BackendsStatusUpdate(appyaml.runtime, self.error_fh)
    rpcserver = self._GetRpcServer()
    response = rpcserver.Send('/api/backends/list', app_id=appyaml.application)
    print >>self.out_fh, response
