Request for review (s) - 7198873

[Jon Masamitsu]

NPG: VM Does not unload classes with UseConcMarkSweepGC

If CMS is not doing class unloading, don't start a concurrent
collection for classloader (and metadata) collection (since
it won't happen without class unloading).

http://cr.openjdk.java.net/~jmasa/7198873/webrev.00/

Also, refactored the code for readability and guarded extra
output with Verbose.

Thanks.

Jon