Review request: 8026781: Add missing test to exercise -XX:+UseLargePagesInMetaspace

[Stefan Karlsson]

http://cr.openjdk.java.net/~stefank/8026781/webrev.00/

The flag -XX:+UseLargePagesInMetaspace was added in the fix for:
8024547: MaxMetaspaceSize should limit the committed memory used by the 
metaspaces

However, we currently have no continuously running tests that turn this 
flag. The added tests, TestSystemGC.java, does the bare minimum and 
starts the JVM with -XX:+UseLargePagesInMetaspace and calls System.gc().

I've taken the liberty of creating a generic System.gc() test instead of 
a more specialized UseLargePagesInMetaspace tests, and added some extra 
run targets to run System.gc() with our different GCs.

thanks,
StefanK