fix timeout

Handel timeout
Go http package has three kind of timeout mechanism:

`dialTimeout` is the timeout for setting up the initial tcp connection. 
This should not exceed 3 * RTT.

`responseHeaderTimeout` is the timeout for receiving the http header. 
This should not exceed `dailTimeout` + 1 * RTT

`transportationTimeout` is the timeout for receiving the actual http body. 
This should not exceed `electionTimeout`