RFR : 7902707 : user modules can be used only in othervm

[Igor Ignatyev]

http://cr.openjdk.java.net/~iignatyev//CODETOOLS-7902707/webrev.00
> 230 lines changed: 175 ins; 27 del; 28 mod;


Hi all,

could you please review this patch which makes it possible to use user modules in agentvm?
from JBS:
> usage of user modules leads to CNF if a test is run in agentvm, because jtreg doesn't communicate module path to agents. 
> 
> A similar problem exists in driver actions, even in othervm execution mode, as DriverAction filters out --module-path and other related flags (rerun section, though, has them listed which made it hard to comprehend) 

the patch include the following changes:
 - extend DO_MAIN operation message to include module-path and add-module list; 
 - if an agent gets a not empty modulepath, it constructs ModuleLayer is constructed using this path, and uses the loader from this layer instead of system loader;
 - --module-path and --add-module are recorded in rerun section; 
 - for driver, --module-path, --add-modules, --add-exports, --add-opens are exempted from filtering.

I should notice that the driver part change is debatable, yet I'd argue the new behavior doesn't contradict the tag spec or any other official jtreg documentations and is less surprising.

JBS: https://bugs.openjdk.java.net/browse/CODETOOLS-7902707
webrev: http://cr.openjdk.java.net/~iignatyev//CODETOOLS-7902707/webrev.00

Thanks,
-- Igor