As discussed in http://n4.nabble.com/Hudson-and-Selenium-Unable-to-determine-the-host-name-Skipping-Selenium-execution-tp956619p956791.html some operations and plugins can fail due to the way Computer.getHostName works - basically Hudson thinks it is unable to ping a slave even though the slave really is reachable from the master.

This patch turns the way a slave is pinged into an extension point so people can implement custom ways of pinging - for example calling out to the ping command of the OS. An implementation of the extension point is included that maintains the current mechanism, so by default there should be no change in behavior.

The extension-point/default-implementation approach follows the pattern of the ssh-slaves plugin, which uses an extension point in locating a JVM on the slave.