RFR: Reorganize jmh-jdk-microbenchmarks for version specific directories

[Eric Caspole]

Hi everybody,

Could I have reviews on this modification of the existing project to 
support JDK version specific microbenchmarks? Only a few new files are 
added to make a placeholder for micros-jdk9, where I soon plan to add 
some new ones.  All the existing ones are in now micros-jdk8. This 
change allows people to continue to easily build on and work with JDK 8 
only if desired while allowing for new development.

http://cr.openjdk.java.net/~ecaspole/jmh_version_specific/webrev/

Thanks,

Eric