Bug 1087630 - [Autolander] use integration branch, add tests

This is not perfect and we can make it better, but some feedback would be good if you guys have any. Here is a few things at a high-level of what's done here:

* Taskgraphs - Schedules tasksgraphs if the project contains a taskgraph.json. Will wait until a "finished" state to land. If there is no taskgraph.json, lands when the bug has checkin-needed and a review. 
* Integration Branch - Commits are applied to the integration branch. In the case of a taskgraph failure the integration branch is re-built and commits are re-played on top of it.
* Integration Tests - End-to-end integration tests have been implemented. Each test currently destroys and re-creates a test repo on github. Run tests using ```npm test```.

https://bugzilla.mozilla.org/show_bug.cgi?id=1087630
This scope is needed on the task-graph, level to create a task in the task-graph that has the given route. It's not required on the task-level.

But are creating this route on task-graph level, do you really need or even want the route on task-level?
From what I can see you're only listening for `taskcluster.SchedulerEvents`:
https://github.com/KevinGrandon/autolander/blob/bug_1087630_autolander_integration_branch/lib/task_pulse.js#L21