RFR(S/M) : 8243430 : use reproducible random in :vmTestbase_vm_gc

[Igor Ignatyev]

http://cr.openjdk.java.net/~iignatyev/8243430/webrev.00
> 555 lines changed: 11 ins; 65 del; 479 mod;

Hi all,

could you please review this small patch?
from JBS: 
> this subtask is to use j.t.l.Utils.getRandomInstance() as a random number generator, where applicable, in : vmTestbase_vm_gc test group and marking the tests which make use of "randomness" with a proper k/w.

testing: : vmTestbase_vm_gc test group
JBS: https://bugs.openjdk.java.net/browse/JDK-8243430
webrevs:
- code changes: http://cr.openjdk.java.net/~iignatyev//8243430/webrev.00.code
> 94 lines changed: 11 ins; 65 del; 18 mod;
- adding k/w: http://cr.openjdk.java.net/~iignatyev//8243430/webrev.00.kw
> 229 lines changed: 0 ins; 0 del; 229 mod; 
- full: http://cr.openjdk.java.net/~iignatyev//8243430/webrev.00
> 555 lines changed: 11 ins; 65 del; 479 mod;

Thanks,
-- Igor