RFR (XS) - 8176827 Test can't find libXext.so

[Ioi Lam]

Hi,

JDK-8176827 is a closed issue, but basically we have some tests that 
have unnecessary dependencies on desktop features, and would 
sporadically fail on hosts that are  configured to run only headless tests.

https://bugs.openjdk.java.net/browse/JDK-8176827
http://cr.openjdk.java.net/~iklam/jdk10/8176827-cant-find-libxext.v01/

The fix is simple -- replace desktop classes used by the tests with 
headless classes. E.g., java.awt.Button -> java.util.logging.Level

Thanks
- Ioi