Replace coversRegion for coversAtLeastRegion

The flickerlib now supports coversAtLeastRegion and coversAtMostRegion to determine the minimum/maximum area covered by a set of layers.

Update tests to invoke the new method

Test: atest FlickerTests
Change-Id: I3bc8f10745beb4776fc03a70adf866fdcea8d8af
2 files changed