Added runOnce Task for CI integration

Important: running npm install karma-junit-reporter is also necessary.

Since it is a task you can simply start it using:
```
grunt runOnce
```
Remark: Since I test on a slower machine, I moved the karma start up a bit, since port check appears not to ensure karma is ready.

BTW: If you change it to singleRun, I don't care at  all ;-)