Buildbot upgrade

We are currently running a modified version of buildbot (available at https://github.com/vladbogo/buildbot). This prevents us from easily upgrading buildbot.

Steps:
1. MTR step was removed from buildbot starting version 3.0, so we need to define and use that as a custom step.
2. Create buildbot PRs with other changes and re-asses what happens if those are not accepted
3. Identify other potential issues