[taskcluster] Create a check that test a task end to end

[Benson Wong]

• Define specific index string (eg. "check.task.e2e")
• Query index to obtain task ID
• If no task, create a new task, specifying index route
• If task has completed, then download artifact, and create a new task
• If task has pending state, and is less than X minutes old, then do nothing

This check verifies that:

• task can be created
• index is listening to index.* topics on pulse
• artifacts are published on store

[Mathieu Leplatre]

We decided to split this into individual checks instead