RFR: 8248346: Move OopStorage mutex setup out from OopStorageSet

[Stefan Karlsson]

Hi all,

Please review this small patch to move the OopStorage mutex creation out 
from oopStorageSet.cpp and put it inside the OopStorage constructor.

https://cr.openjdk.java.net/~stefank/8248346/webrev.01
https://bugs.openjdk.java.net/browse/JDK-8248346

So far I've only tested this locally with gtest. The product code should 
be the same, but the test used slightly different values when 
initializing the mutexes. That doesn't seem to affect the tests.

Thanks,
StefanK