As Gerrit applies result styles based on the first word of the response
from the CI job result, add a 'result_WARNING' style to allow failing
non-voting jobs to specify WARNING as the first word to get a colour
applied that is clearly distinguishable from the text from when the job
passes, while also being different to voting jobs that pass/fail.
Change-Id: I1a9bea0c0830f9ca15f8369632ff2fdbeadada56