Optofidelity: Configurable test-plane

When we want to run tests that tap in certain location of the screen,
we need to adjust the test-plane for those subjects. Otherwise tapping
that location will move the device away from the calibrated location.

BUG=chromium:516704
TEST=Manual test

Change-Id: I348a07a1d10364dad2456207570f544cc4dd3c19
Reviewed-on: https://chromium-review.googlesource.com/336486
Commit-Ready: Dennis Kempin <denniskempin@chromium.org>
Tested-by: Dennis Kempin <denniskempin@chromium.org>
Reviewed-by: Dennis Kempin <denniskempin@chromium.org>