Fix showing custom computer icon in executor status window. If somebody creates a plugin with a custom Computer type and overrides the getIcon() and getIconClassName() methods, the new icon will be displayed in the /computer/ page of Jenkins. However, the executor status window has the default icon hard-coded into it and so it will not be updated.

See: https://github.com/jenkinsci/jenkins/blob/master/core/src/main/resources/lib/hudson/executors.jelly#L37
https://github.com/jenkinsci/jenkins/blob/master/core/src/main/java/hudson/model/Computer.java#L730