Tile qa plot v6

[araichoor]

This PR adds few safety checks around the cutout displaying in the tile-qa*png file, as this has been causing some issues (#1563, #1576).
As said in #1563, the root cause of the problem is not clear to me, but hopefully those changes should handle those.

Besides, I've taken advantage of the introduction of the use of log(), to change some print() to log.info() or log.warning().

[coveralls]

Coverage decreased (-0.02%) to 25.304% when pulling 2329917 on tile_qa_plot_v6 into 7bdae16 on master.