RFR: 8061219: Implement unit-tests for UL

[Marcus Larsson]

Hi,

Please review the following patch to add unit tests for the unified 
logging framework. Tests are written for the new gtest unit test 
framework. Most of the public functions for UL should be covered, but 
later additions have internal vm tests (in log.cpp) that will be ported 
separately.

Webrev:
http://cr.openjdk.java.net/~mlarsson/8061219/webrev.00/

Issue:
https://bugs.openjdk.java.net/browse/JDK-8061219

Testing:
New tests through JPRT

Thanks,
Marcus