[FIXED JENKINS-11130] SEVERE: I/O error in channel Chunked connection when using jenkins-cli.jar

When using HTTP full duplex connections the upstream channel can be idle for
long periods of time and the webserver will time the connection out. Jenkins
sees this and terminates the downstream channel causing the unexpected closure
of the read channel in the CLI client.

Timeout of 15 seconds is based on the 20 second default timeout as seen in
Ubuntu Oneiric Tomcat 6 installations.