Don't bail out early when only some of the spec paths map to files

[lvh]

I'm not sure if this is a bug, but it's behavior I'm seeing in other tools :) Suppose if you have some tests in native JS and some in Coffeescript that get compiled down to JS. A sensible specs definition would be:

  specs: [
    './test/integration/*.js',
    '.tmp/integration/*.js'
  ],

... but protractor bails out early if './test/integration/*.js' doesn't match any tests. I was hoping for a warning instead.