Scope yarn and npm settings inside node closure

[srs]

Scope yarn and npm settings inside node closure. Like this:

node {
  version = 'x.x.x'
  download = true

  npm {
    version = 'x.x.x'
    workDir = ...
  }

  yarn {
    version = 'x.x.x'
    workDir = ...
  }
}

[srs]

Should also probably do the same for grunt and gulp.

node {
  ...
  grunt {
    enabled = true
    ...
  }

  gulp {
    enabled = true
  }
}