rework python scripts to support Python 2 & 3 We run the unittests in both python versions to maintain coverage, and we run things through `cros lint` during upload to help prevent regressions. We also switch the default to Python 3 to keep people on their toes. BUG=chromium:982465 TEST=running unittests against python2 & python3 pass TEST=`./fmap.py bin/example.bin` through python2 & python3 works Change-Id: I79f0ce59664ea42dfa18e45ccde0dffc0c18227d Reviewed-on: https://chromium-review.googlesource.com/1693888 Tested-by: Mike Frysinger <[email protected]> Commit-Ready: Mike Frysinger <[email protected]> Legacy-Commit-Queue: Commit Bot <[email protected]> Reviewed-by: Duncan Laurie <[email protected]>