netty transport: set quiet period to zero.

Disable grace peiod in EventLoopGroup.shutdownGracefully() so that boss
group and worker group get shut down immediately.
Merge pull request #166 from m1ch1/master

netty transport: set quiet period to zero.
Add retry logic for joining.

The joiner might start before the cluster gets start. The joiner will try to
re-join the cluster if it can't connect to the cluster.