8194937: Inconsistent behavior of --validate-modules when combined with -m and other options

[Alan Bateman]

The java `--validatate-modules` option is a very useful option to scan 
all modules to identify a wide range of issues such as conflicts, 
duplicate modules in a directory, modules shadowed by modules of the 
same name, malformed module descriptors and more.

We originally implemented this option as "launcher helper" where it runs 
after the VM is started. This creates a chicken 'n egg scenario where 
starting the VM might fail due to issues that the validation should 
catch. To avoid that, the VM starts up with a minimal boot layer, just 
java.base, which is enough to allow the launcher helpers to run before 
the launcher exits. This works okay but it the effect of ignoring 
options such as --add-modules and -m that would normally specify the 
module roots. This just means that f you specify any of these options 
with --validate-module then the module path will be validated as 
expected but bad values specified to these other options are ignored.

To get the option handling consistent, I'd like to move the validation 
from being a launcher helper so that it runs as part of the module 
system initialization (only when --validate-module is specified of 
course).  This allows the option to be combined with other options that 
specify module name. It also allows the option to be used with other 
"exiting options" such as -version, --list-modules and --describe-module.

The webrev with the changes is here. Note that the validation has not 
changed, this is mostly a house move with some expansion of the tests to 
cover combinations of options that we didn't test in the original 
implementation.
     http://cr.openjdk.java.net/~alanb/8194937/webrev/

-Alan