set the environment for the supervisord process

If the supervisord.conf only has an extending rpcinterface, pay attention, **there is not any section [program:xxx]**, in this case, self.environment (the environment of ServerOptions) will never be assigned a value, which leads to two problems:

* the extending rpcinterface can not get the environment from os.environ
* the following function seems useless because **self.environment** never be assigned and **self.environment is None** 

    def process_environment(self):
      os.environ.update(self.environment or {}) 

This patch will fix this.