Add number of zuul job attempts to logstash events

This will help us better track how often jobs are being rerun. We should
be able to query for numeric values of this field and count the number
of jobs that had more than one attempt. From that we should also be able
to identify if specific jobs hit these problems more than others.

Change-Id: I6ad21ad3a55140356b9a5f19e5e5bb83663898f3

roles/submit-log-processor-jobs/library/submit_log_processor_jobs.py

@@ -166,6 +166,8 @@ class LogMatcher(object):
         fields["log_url"] = log_url
         if 'executor' in zuul and 'hostname' in zuul['executor']:
             fields["zuul_executor"] = zuul['executor']['hostname']
+        if 'attempts' in zuul:
+            fields["zuul_attempts"] = zuul['attempts']
         return fields