RFR(S) : 8234290 : compiler/c2/Test6857159.java times out and fail to clean up files

[Igor Ignatyev]

http://cr.openjdk.java.net/~iignatyev//8234290/webrev.00/index.html
> 67 lines changed: 16 ins; 24 del; 27 mod;

Hi all,

could you please review this small fix for Test6857159 test?
from JBS:
> the test has -XX:CompileOnly=compiler.c2.Test6857159$Test$ct::run, but there is no 'ct' class, there are ct[0-2], and ct0 the only which has 'run' method. shouldNotContain("COMPILE SKIPPED") and shouldContain("$ct0::run (16 bytes)"), which, I guess, were a defense against such situation, didn't help b/c PrintCompilation output doesn't have 'COMPILE SKIPPED' lines and have 'made not compilable on levels 0 1 2 3 ... $ct0::run (16 bytes) excluded by CompileCommand' line.
the patch fixes CompileOnly value (actually replaces it w/ the correct CompileCommand), removes extra layer, and makes the test to use WhiteBox to check if ct0::run got compiled.

webrev: http://cr.openjdk.java.net/~iignatyev//8234290/webrev.00/index.html
JBS: https://bugs.openjdk.java.net/browse/JDK-8234290
testing: 
 - compiler/c2/Test6857159.java once on linux-x64,windows-x64,macosx-x64
 - compiler/c2/Test6857159.java 100 time on windows-x64-debug (where all failures were seen so far)

Thanks,
-- Igor