Make Jetty Session ID configurable via System properties

Executables WAR enforces random cookies, which is not comfortable in some cases (e.g. when you define your Jetty session manager). There are also issues like JENKINS-25046

It would be great to have an option to opt-out from the default behavior and to delegate decision to Jetty.

Another use-case is to be able to specify a custom cookie name via system property.