feature request: Add support for process.env.npm_config_node_gyp

[ktrzeciaknubisa]

As we have noticed in jxcore/jxcore#678, the node-gyp finding pattern is not sufficient if one would call e.g.:

$ jx install dtrace-provider
> dtrace-provider@0.6.0 install ...
> jx scripts/install.js

cannot locate npm install

This happens when there is no node-gyp and/or npm available under /usr/local/lib/node_modules/.

Therefore I'd like to propose adding support for process.env.npm_config_node_gyp which is a result of implementing npm install --node-gyp=<path-to-custom-node-gyp> by npm team: npm/npm#4887 .

Thus scripts/install.js of dtrace-provider would have this added:

if (process.env.npm_config_node_gyp && fs.existsSync(process.env.npm_config_node_gyp))
  nodegyp = process.env.npm_config_node_gyp;

[melloc]

From jxcore/jxcore#678 it sounds like you fixed this by changing it to call npm-cli.js instead. After the fix for #95 (which was released in dtrace-provider@0.8.3), this library uses the node-gyp in the PATH, which should also take care of fixing this issue.