Support prebuild mirrors config

[fengmk2]

https://github.com/mafintosh/prebuild/blob/master/util.js#L37

Take leveldown for example:

leveldown's package.json

  "scripts": {
    "install": "prebuild --install",
    "test": "mocha --expose-gc --slow 2000 --timeout 600000"
  },

$ npminstall -c

/path/to/prebuild-mirror-config.json example:

{
  "leveldown": {
    "binary": {
      "host": "https://npm.taobao.org/mirrors/leveldown"
    }
  },
  "couchbase": {
    "binary": {
      "host": "https://npm.taobao.org/mirrors/couchbase"
    }
  },
  ...
}

[fengmk2]

cnpm/mirrors#91

[fengmk2]

This can also work for node-pre-gyp https://github.com/mapbox/node-pre-gyp/blob/master/lib/util/versioning.js#L277

https://github.com/mapbox/node-sqlite3/blob/master/package.json#L52

"scripts": {
        "prepublish":"npm ls",
        "install": "node-pre-gyp install --fallback-to-build",
        "pretest": "node test/support/createdb.js",
        "test": "mocha -R spec --timeout 480000"
    },