Improve calibration and accouting in flush-finish tests

 * Verify stability of calibration by running 3 samples with maximum
load and verifying that they are within 10% of projected time.

 * Retry calibration up to 5 times if calibration or verification fails.

 * Do not count submit time into wait time as submit cost can be
relatively high on low-end devices.

Bug: 22301848
Change-Id: Iff4523f601edcdec1375662a065bf50b8970ef02
1 file changed