Initialize supervisor RPC.

        Allow passing in an RPC connection, or a port number for
        making one.

def _init_supervisor_rpc(self, rpc_or_port):
        '''Initialize supervisor RPC.

        Allow passing in an RPC connection, or a port number for
        making one.

        '''
        if isinstance(rpc_or_port, int):
            if self.username:
                leader = 'http://{self.username}:{self.password}@'
            else:
                leader = 'http://'
            tmpl = leader + '{self.name}:{port}'
            url = tmpl.format(self=self, port=rpc_or_port)
            self.rpc = xmlrpc_client.ServerProxy(
                url, transport=TimeoutTransport())
        else:
            self.rpc = rpc_or_port
        self.supervisor = self.rpc.supervisor