fix(carousel): replaced $timeout with $interval when it was wrong

I had a to tweak a bit two tests since $interval never throws an exception after flushing, hope I did it OK. 

This addresses #2454
This test now needs `$interval.flush(5000);` here to actually test these values.
I found that this actually causes the test to fail on $interval function because it's calling $interval with `false` as the timeout.