build,tools: make addons tests work with GN

[zcbenz]

This PR refactors the install and build_addons scripts so they can be reused by node-ci and electron projects to build the addons tests.

In detail, this PR does following things:

1. Minor modifications of the GN configurations to fix loading native modules.
2. Add some flags to tools/install.py script to allow customize locations of config.gypi, v8, etc. With some refactoring to remove global variables.
3. Rewrite the tools/build_addons.py script:
   1. Rewrite it from js to python, because implementing cmd args handling with vanilla Node.js would take much longer time than a simple rewrite.
   2. Add a few more flags to make it easier to use for embedders.
4. Modify the Makefile to generate headers in out dir first, and then calls build_addons.py --headers-dir=out_dir/headers (which calls node-gyp --nodedir=out_dir/headers) to build addons. Previously the build system was just calling node-gyp --nodedir=., which relied on quirky behavior of node-gyp and did not really test whether the generated headers work.

Users that rely on make or vcbuild.bat to work on Node are not affected.

[nodejs-github-bot]

Review requested:

• @nodejs/tsc

[zcbenz]

I have separated some changes out of this PR so review should be easier.

/cc @nodejs/gyp @joyeecheung@richardlau for reviewing changes on tools.

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/55698/

[zcbenz]

Ping @nodejs/gyp @joyeecheung@anonrig for review after the holiday.

[joyeecheung]

LGTM % a correction but I think ideally we should have someone from @nodejs/build to confirm that it works with our releases.

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/56066/

[batrla]

Sorry to report it, but this PR caused regression, build in --shared mode now fails:

11:02:41: stdout installing /some_dir/build/prototype/i386/some_bindir/node 11:02:41: stderr Traceback (most recent call last): 11:02:41: stderr File "/some_dir/build/amd64/tools/install.py", line 419, in <module> 11:02:41: stderr run(parse_options(sys.argv[1:])) 11:02:41: stderr File "/some_dir/build/amd64/tools/install.py", line 372, in run 11:02:41: stderr files(options, install) 11:02:41: stderr File "/some_dir/build/amd64/tools/install.py", line 179, in files 11:02:41: stderr action(options, [os.path.join(output_prefix, output_lib)], 11:02:41: stderr ^^^^^^^^^^^^^ 11:02:42: stderr UnboundLocalError: cannot access local variable 'output_prefix' where it is not associated with a value 

The problem in source code is obvious, the variable 'output_prefix' is only defined in some branches.
Later in code the variable is used in a branch where it was not defined before.

[zcbenz]

Sorry for breaking it! I'll create a fix soon.