RFR: 8165700: Convert LogMessage internal tests to GTest

[Marcus Larsson]

Hi,

Please review the following patch converting multiline-logging internal 
VM tests to GTest.

Webrev:
http://cr.openjdk.java.net/~mlarsson/8165700/webrev.00/

Issue:
https://bugs.openjdk.java.net/browse/JDK-8165700
(separated from https://bugs.openjdk.java.net/browse/JDK-8165600 for 
easier reviewing)

Thanks,
Marcus