parse_news.py: [backend] for a suspect build, ensure we have builds for the changeset before it

[jmaher]

many times we find a regression that is for a specific revision. unfortunately we don't have data for changesets prior, sometimes 3 or 4 changesets.

There are 2 things to sort out here:

1. we didn't do the platform build
2. we did the build, but didn't run the perf test

For item #1, we don't build desktop builds for android only (*.java) changes. Likewise some b2g specific changes or test-only changes.

This is why I don't want it to be automatic, but I would like to have a one click button to bring me to a way to launch a build if it is missing. If we do a build, most likely we will run the talos test that was missing. Also in this case we need to context switch out for 3-5 hours until the build is done (pgo takes even longer).

For item #2, we can easily trigger the talos job that wasn't run.

Lastly to reduce the effect of noise, I always do 3 retriggers of each job (2 prior, the suspect changeset, 1 after).

Here is a reference to the arbitrary build scheduler:
http://johnzeller.com/blog/2014/03/12/triggering-of-arbitrary-buildstests-is-now-possible/

Ideally this would be a single click button so we could sanity check we are doing the right thing before scheduling a bunch of jobs.

[jmaher]

this has been filed in bugzilla as:
https://bugzilla.mozilla.org/show_bug.cgi?id=1033657