Connection Broken Pipe Issue

[zwx14700]

Problem description
Currently, the connection_pool doesn't have the mechanism to check whether the connection is closed by the server, which would let write/read have a broken pipe issue.

Problem location
ConnectionPool.

Suggestions for an improvement
There are many discussion in the Tokio repo, and Tokio doesn't have an easy way to check the TCPStream is closed.
websockets-rs/rust-websocket#136
tokio-rs/tokio#483
tokio-rs/tokio#2228

Currently, we can use https://docs.rs/tokio/0.2.16/tokio/net/struct.TcpStream.html#method.poll_peek
to resolve this issue.
If the poll_peek returns 0, that means the socket is closed by the server.