findmissing: Extract decorator functions from main.py

We'll need the decorator functions from multiple places,
so move them into a new file, util.py. While at it, replace print
functions in moved code with logging.

BUG=None
TEST=Run on GCE

Change-Id: I8d45b4f8c1604ee2ef3d394a61c909c3cfb6f527
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2200139
Reviewed-by: Curtis Malainey <cujomalainey@chromium.org>
Commit-Queue: Guenter Roeck <groeck@chromium.org>
Tested-by: Guenter Roeck <groeck@chromium.org>