fix early termination of runs caused by ramp_time > runtime

If ramp_time was longer than the runtime, then the run terminated immediately
after the ramp_time was exceeded. In order to avoid this, teach
runtime_exceeded about ramp_time.

Signed-off-by: Steven Noonan <snoonan@amazon.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>