defined "options.output" to write result in a file

**INPUT**
sample Gruntfile.js config

```
...
        protractor: {
            options: {
                configFile: 'test/protractor/conf.js',
                args: {
                    baseUrl: 'http://localhost:18000',
                    browser: 'phantomjs'
                },
                output: 'build/artifacts/test/protractor/results.tap'
            }
        }
...
```

**OUTPUT**
sample output result
```
$ cat build/artifacts/test/protractor/results.tap
1..2
ok 1 test page should have a title in the page
ok 2 test page should have value "signedin" after clicking .authState() button
# tests 2
# pass 2
# fail 0
```