Pass specified command line params to the subprocess

This commit makes the protractor task pass parameters used to start the Node
process to its background subprocess. This is required e.g. to be able to use
the --harmony flag.

Similar pull request for Grunt itself (already merged):
https://github.com/gruntjs/grunt/pull/877

Should I test it somehow? No current tests seem to actually fire the task from the command line so that might not be easy.