paycheck: Small improvements to the block tracer utility.

This prepends the current block number to the output, simplifies some
logic, and tightens argument validation in the command-line parser.

BUG=None
TEST=paycheck -B/-b works.

Change-Id: I90d5cdf721612cdd12e49f4e4181849fc699807f
Reviewed-on: https://chromium-review.googlesource.com/286547
Tested-by: Gilad Arnold <garnold@chromium.org>
Commit-Queue: Gilad Arnold <garnold@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>
2 files changed