test: Add a test for log filter-*

This exercises a few success and failure modes of the log filter-*
commands. log filter-list is not tested because it's purely informational.
I don't think there's a good way to test it except by testing if the output
of the command exactly matches a sample run.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>