patchtest-send-results: check max line length, simplify responses

Check that the maximum line length of the testresult file is less than
220 characters, to help guard against malicious changes being sent in
email responses. If any line exceeds this length, replace the normal
testresults used in the response with a line stating that tests failed,
but the results could not be processed. Also clean up the respone
substrings slightly to go along with the change.

Signed-off-by: Trevor Gamblin <tgamblin@baylibre.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>