Avoid using sun.misc.VM

The function org.infinispan.container.entries.PrimitiveEntrySizeCalculator.IntegerCacheConstraints.calculateMaxIntCache() is using sun.misc.VM.

This class is being moved and "idden" in Java 9:

• http://mail.openjdk.java.net/pipermail/core-libs-dev/2016-January/037853.html

Could we try avoiding the need for this, or explore alternatives?

One could use reflection to see if the class is available without loading it explicitly, but that still needs some sensible fallback for the case in which the class isn't available.

Even if this looks like a small detail, this completely blocks the possibility to test Infinispan on Java 9.