789935 - stop hardcoding Try tree name in try mailing code

Status: RESOLVED INCOMPLETE

(Release Engineering :: General, enhancement, P3)

Description

[[e-mail] (:bhearsum)]

Right now, things are hardcoded to work with the "Firefox" product. bug 749151 will change it to hardcode some exceptions to make it work with Thunderbird too. Eventually it will need to work with B2G and probably other things. We should stop hardcoding all over the place and centralize this info in production-branches.json

Roughly, we need to:
* Add support for 'tree' as an arg to makeTryMessage and buildTryChangeMessage
* Add a 'tree' parameter to https://github.com/mozilla/build-tools/blob/master/buildfarm/maintenance/production-branches.json
* Pass the path to that file to postrun.py (https://mxr.mozilla.org/build-central/source/buildbot-configs/mozilla-tests/tests_master.cfg#33, https://mxr.mozilla.org/build-central/source/buildbot-configs/mozilla-tests/universal_master_sqlite.cfg#33, https://mxr.mozilla.org/build-central/source/buildbot-configs/mozilla/builder_master.cfg#43, https://mxr.mozilla.org/build-central/source/buildbot-configs/mozilla/universal_master_sqlite.cfg#43)
* Read it where necessary, pass it along to makeTryMessage
* Pass "tree info" or something similar to generate* in misc.py and have it look it up and pass it along to buildTryChangeMessage