RFR: 8015784: Add configure parameter --with-update-version

[Tim Bell]

Erik:

> Please review this patch from Tristan Yan.
>
> The Oracle build promotion process requires customization of the 
> JDK_UPDATE_VERSION for certain test builds. In the old build this was 
> done by setting the variable in the environment. This patch adds a 
> configure parameter to override the value of the update version.
>
> http://cr.openjdk.java.net/~erikj/8015784/webrev.root.01/

Looks good to me.

Tim