update_payload: Move minor version checks to CheckOperation.

Various small fixes. Move checks for operation and minor version
compatibility to CheckOperation.

BUG=none
TEST=`./checker_unittest.py` and running paycheck on payloads.

Change-Id: I6abd0ec200c1d4d885b09dfb84ee7e6cfad4172c
Reviewed-on: https://chromium-review.googlesource.com/254345
Reviewed-by: Allie Wood <alliewood@chromium.org>
Commit-Queue: Allie Wood <alliewood@chromium.org>
Trybot-Ready: Allie Wood <alliewood@chromium.org>
Tested-by: Allie Wood <alliewood@chromium.org>
2 files changed