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
Is there any reason this if statement was moved from the restartTimer above?
This was meant to check that the interval created makes sense, it seems unsafe to remove it from line 109. An additional check here may make sense, but I think it should also still be left intact above.