Allows both dashes or underscores for v8flag word separator.

[sttk]

In Node.js API document, there is a description that:

Note: V8 options allow words to be separated by both dashes (-) or underscores (_).
For example, --stack-trace-limit is equivalent to --stack_trace_limit.

This pr is for supporting this.

[phated]

@sttk has node supported this since 0.10 or maybe it only supported underscores?

@tkellen is this something we want to support?

[sttk]

@phated Yes. v0.10 supports this specification. Following is the result I tried:

$ cat test.js
const s = 'hello';
console.log(s);
$ node -v
v0.10.48
$ node test.js
hello
$ node --use_strict test.js

/Users/sttk/test.js:1
(function (exports, require, module, __filename, __dirname) { const s = 'hello
                                                              ^^^^^
SyntaxError: Use of const in strict mode.
    at Module._compile (module.js:439:25)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Function.Module.runMain (module.js:497:10)
    at startup (node.js:119:16)
    at node.js:945:3
$ node --use-strict test.js

/Users/sttk/test.js:1
(function (exports, require, module, __filename, __dirname) { const s = 'hello
                                                              ^^^^^
SyntaxError: Use of const in strict mode.
    at Module._compile (module.js:439:25)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Function.Module.runMain (module.js:497:10)
    at startup (node.js:119:16)
    at node.js:945:3
$ # Execute with unsupported flag
$ node --use--strict test.js
Error: unrecognized flag --use--strict
Try --help for options
hello
$

[phated]

@sttk any idea why this is failing?

[sttk]

The reason of failing in this and other PRs is only timeout. In my travis test, those tests succeeded.

This timeout is caused in the same test case and it is the first test case using child_process.exec.
Since It simply executes ./test/bin/respawner.js which is used other test cases, I think that first child_process.exec spent a lot of time.

We may need to set timeout longer for this test case or on the whole.

[phated]

Cherry-picked as c787fb1