Cleanup messageFormatter example to use logs from build steps instead…

… of directly using build logs

master/docs/manual/cfg-statustargets.rst

@@ -1060,8 +1060,8 @@ For example, if only short emails are desired (e.g., for delivery to phones) ::
                      messageFormatter=messageFormatter)

Another example of a function delivering a customized html email
containing the last 80 log lines of logs of the last build step is
given below::
containing the last 80 log lines of logs of the last build step that
finished is given below::

    from buildbot.status.builder import Results

@@ -1122,8 +1122,18 @@ given below::
                            text.append(u'<tr><td>%s:</td></tr>' % file['name'] )
                        text.append(u'</table>')
            text.append(u'<br>')
            # get log for last step
            logs = build.getLogs()
            # get all the steps in build in reversed order
            rev_steps = reversed(build.getSteps())
            # find the last step that finished
            for step in rev_steps:
                if step.isFinished():
                    break
            # get logs for the last finished step
            if step.isFinished():
                logs = step.getLogs()
            # No step finished, loop just exhausted itself; so as a special case we fetch all logs
            else:
                logs = build.getLogs()
            # logs within a step are in reverse order. Search back until we find stdio
            for log in reversed(logs):
                if log.getName() == 'stdio':