RFR: 8149128: Add tests for G1MMUTracker

[Erik Helin]

Hi all,

we have a new shiny unit test framework so I figured I would take it for
a spin. I added some new tests for G1MMUTracker, see below. If you want
to try out the new test runner, just apply the patch, then:

  $ make test-hotspot-gtest

Enhancement:
https://bugs.openjdk.java.net/browse/JDK-8149128

Webrev:
http://cr.openjdk.java.net/~ehelin/8149128/00/

Testing:
- JPRT
- Running locally on Linux x86-64

Thanks,
Erik

PS. I don't really how if the feature complete applies to tests?