RFR: 8026789 Update test/java/lang/instrument/Re(transform|define)BigClass.sh test to use NMT for memory leak detection

[Staffan Larsen]

The two tests currently use /proc/self/stat to read the virtual memory usage for the process. This only works on linux and only gives a single  value to analyze. NMT works on all platforms and gives a lot more detail about where the memory is consumed. 

Without this fix, I can repro JDK-8023201 when stressing the machine heavily, but with this fix the test passes. The reason for this is probably that NMT uses a more granular measurement of committed memory, and not that the VM actually uses less memory. I have retained the memory growth limit of 32MB, but if that is a good value or not, I don't know. When stressing the test, I see NMT reporting about 1MB in committed memory growth. 

I have also removed the tests from ProblemList.txt. 

webrev: http://cr.openjdk.java.net/~sla/8026789/webrev.00/
bug: https://bugs.openjdk.java.net/browse/JDK-8026789

Thanks,
/Staffan