fix android swipe duration

* the swipeStepsPerSec value was wrong. Android docs says it's about 200 steps per sec. Using a bunch of different swipe times and linear regression I determined it to be about 28 on my GPU-enabled emulator. Not sure if this varies widely for others.
* the logic for converting duration to steps was wrong and has been fixed
* I took out a needless post-swipe timeout. I don't think uiautomator actually returns control before the swipe is done

WARNING: this might require testers to change swipe durations if tests rely on them.