tests: add `NOMATCH` test result

tests: add `NOMATCH` test result

Currently, there are two supported test results: `OK` and `FAIL`.  It is
expected that either the iptables command fails, or it succeeds and
dumping the rule has the correct output.  However, it is possible that
the command may succeed but the output may not be correct.  Add a
`NOMATCH` result to cover this outcome.

Make a few white-space improvements at the same time.

Signed-off-by: Jeremy Sowden <jeremy@azazel.net>
Signed-off-by: Florian Westphal <fw@strlen.de>