* Change the api of the SLA classes:
- add_iteration() - processes a single iteration result from the queue
- result() - return the SLAResult based on the data processed so far.
It now also returns a successful result in case there was no iterations
data.
* Add a new SLAChecker class:
- add_iteration() - processes a single iteration result with different SLAs
- results() - return cumulative SLA results for all SLAs
* Change the benchmark engine so that it supports scenario runner aborts
on SLA failure
* Support the "abort on SLA failure" feature in the CLI:
rally task start ... --abort-on-sla-failure
* Modify the SLA detailed messages (cleaner text and less decimal places)
* Update unit and functional tests correspondingly. Also remove the usage of the
deprecated "max_failure_percent" SLA from the functional tests.
Change-Id: I91894a81649815428fd1ac7afcfce9cf47160fc9
1fc89d3931