install-test: fix shrinkwrap handling of package-lock.json

[raymondfeng]

For a simple project with .npmrc containing 'package-lock=false',
npm install-test command will generate package-lock.json.*.

If there is an existing package-lock.json, npm install-test triggers
lifecycle actions twice for both install and test.

The problem can be reproduced by the following package.json and npm it

package.json
{
  "name": "t",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo TEST"
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
    "debug": "^3.1.0"
  }
}

[raymondfeng]

@zkat Any chance to review the PR? npm install-test is pretty much broken with package-lock ATM.

[zkat]

wow I'm the worst 4df5934

Thanks for this patch! haha

[bajtos]

@zkat is it possible to back-port this change to the npm version line 5.6 that's shipped as part of Node.js 8.x LTS, please? How can I help to make this happen?