- Avoid using a temporary variable where not necessary
- Use fewer, better stubs in the tests to avoid warnings and better
  test the implemented functionality.

to fix issues with shwoing npm debug output even on non-verbose install runs.

instead of writing a .npmrc file, which simplifies the code.
npm_cache_config is still preserved for backwarts compatiblility and
usage int he kibana@n formulas in core.

This tells npm pack to don't run prepublish scripts at all.
I think this is the best default because:
* most modules don't have a prepublish script at all and aren't affected
  by this change
* most prepublish scripts are calling devDeps, which would fail in our
  case, because (dev)Deps aren't installed at npm pack time until #2820
  gets resolved
* we favor npm registry tarball for formula downloads, which are already
  prepublished, so we would in the best case needlessly run prepublish
  a second time and in the worst case it would fail (because a clean
  step is required before running prepublish a second time in a row)
* This change does the right thing for >99% of all the packages and
  would only affect packages with prepublish scripts downloaded from a
  non-npm registry tarball (like github tarballs) and with a prepublish
  script wich does no't require any devDep (unlike for cross platform)

This makes npm pack to log verbose debug output to the console to
simplify debugging npm pack failures.
Refs: https://github.com/Homebrew/brew/pull/2820#discussion_r123890729
Prevously Utils.popen_read swallowed all debug output.

By telling node-pre-gyp and prebuild to don't pull prebuild binaries and
instead build them from source. This still may not work for some custom
third party scripts for pulling prebuild binaries.

to match the loglevel used in npm_debug.log (previous --verbose loglevel
would match -dd)

[WIP] Added tests for language/java