Add npm_lifecycle_script to env in makeEnv

[adityavohra7]

Summary

Fixes #4003.

The motivation behind this PR is to get more parity with npm wrt the process.env variables available when running scripts.

Test plan

Made these exact changes in my globally installed yarn's node_modules. Using the following package.json

{
  "name": "foo",
  "version": "1.0.0",
  "scripts": {
    "test": "env | grep npm_"
  }
}

I ran yarn test to yield:

MacBook-Pro:temp adityavohra7$ yarn test
yarn test v0.27.5
warning package.json: No license field
$ env | grep npm_
npm_config_version_git_tag=true
npm_config_init_license=MIT
npm_config_registry=https://registry.yarnpkg.com
npm_execpath=/usr/local/lib/node_modules/yarn/bin/yarn.js
npm_config_argv={"remain":[],"cooked":["test"],"original":["test"]}
npm_lifecycle_event=test
npm_package_name=foo
npm_package_version=1.0.0
npm_package_scripts_test=env | grep npm_
npm_config_strict_ssl=true
npm_config_save_prefix=^
npm_config_version_git_message=v%s
npm_lifecycle_script=env | grep npm_
npm_config_user_agent=yarn/0.27.5 npm/? node/v8.4.0 darwin x64
npm_config_ignore_scripts=
npm_config_version_git_sign=
npm_config_ignore_optional=
npm_config_init_version=1.0.0
npm_config_version_tag_prefix=v
npm_node_execpath=/usr/local/bin/node
Done in 0.15s.

npm_lifecycle_script now appears in process.env.

[BYK]

This is already exposed as npm_lifecycle_event on line 50 above. Isn't that enough?

[BYK]

Ah, sorry. I read the original issue now and I understand what this is doing.

[BYK]

LGTM.

@arcanis - any concerns?

[arcanis]

Nope, was waiting for the tests to end. Good to merge!

[adityavohra7]

Wow thanks for the quick review and edits and merge everyone! 😄

[palmerj3]

So I was using process.env.npm_lifecycle_script to determine if it was yarn or npm running the preinstall script. I would use this to subtly educate team members to use Yarn over NPM.

Is there another way I could accomplish this?
@BYK

[adityavohra7]

@palmerj3, maybe npm_config_user_agent or npm_execpath? This SO post seems to suggest the latter.

[palmerj3]

@adityavohra7 cool thanks! Hope my comment didn't seem like I was putting down this PR - you did the right thing :) The link you sent seems like a more proper way to do what i'm looking to do.