Migrate crosdl.py to Python 3

BUG=chromium:1031760
TEST=./crosdl.py --to_stick /dev/null -p peppy -c beta -b 5116.32.0

Change-Id: Id90c01eca73cd9789fc327fd251daba3d995ff2e
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crostestutils/+/1959064
Tested-by: Greg Edelston <gredelston@google.com>
Reviewed-by: Katherine Threlkeld <kathrelkeld@chromium.org>
Reviewed-by: Aviv Keshet <akeshet@chromium.org>
Commit-Queue: Greg Edelston <gredelston@google.com>
1 file changed