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

[Erik Joelsson]

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/

/Erik