Comment 2 for bug 1670577

Thanks Takashi for show me the logstash tool, it's very useful.

I could check with the following query http://logstash.openstack.org/#dashboard/file/logstash.json?query=(message%3A%20%5C%22%5BZuul%5D%20Job%20complete%2C%20result%3A%5C%22%20OR%20message%3A%20%5C%22To%20get%20raw%20JSON%20output%20of%20task%20results%2C%20run%5C%22%20OR%20message%3A%20%5C%22Input%20task%20is%20invalid%5C%22)%20AND%20build_name%3A%20gate-networking-midonet-rally-dsvm-ml2-ubuntu-xenial-nv

that the last rally job that worked was with this commit

9e3ccfa [CI] Update hacking and fix pep8 errors

and the first job failing has this rally commit

732bbc1 Merge "[Core] Make task engine more abstract”