autotest (dhcp): improve dhcp debugging

When we receive an unexpected message, log the type of message
received, and the type expected. This should make it easier to
diagnose failures.

While there: fix some warnings about parameters to loggers.
(Send the parameters through, instead of applying the format
operator.)

BUG=chromium:341946
TEST=network_DhcpRenew, network_DhcpNegotiationSuccess, manual

manual testing: commented out None entry in MESSAGE_TYPE_BY_NUM,
saw network_DhcpNegotiationSuccess fail

Change-Id: Ia10af1d85436953607d0b6592d440ce8d7defe3e
Reviewed-on: https://chromium-review.googlesource.com/185495
Tested-by: mukesh agrawal <quiche@chromium.org>
Reviewed-by: Christopher Wiley <wiley@chromium.org>
Commit-Queue: mukesh agrawal <quiche@chromium.org>
3 files changed