RFR(s): 8151264: Add a notification mechanism for UL configuration changes

[Robbin Ehn]

Hi, please review this minor change.

Bug: https://bugs.openjdk.java.net/browse/JDK-8151264/
Webrev: http://cr.openjdk.java.net/~rehn/8151264/webrev/

Tested with a new internal vm test (included).

Thanks!

/Robbin