Taskcluster-taskgraph

Changed
- BREAKING CHANGE: `TransformConfig.kind_dependencies_tasks` is now a dictionary keyed by task label.
- BREAKING CHANGE: `vcs.head_ref` was renamed into `vcs.head_rev` to clarify that the function returns a revision. This also matches `--head-rev`.
- BREAKING CHANGE: Similarly, `vcs.base_ref` was renamed into `vcs.base_rev`.
- `run-task` now clones all git-submodules at the same time as cloning the base/head repository.
- `run-task` now checks out a revision as a named branch that matches `${PROJECT}_HEAD_REF`
- `head_ref` parameter now points to a named branch and if needed, falls back to the revision hash

Added
- `vcs.get_changed_files()` which returns a list of files that are changed in this repository's working copy.
- `vcs.get_outgoing_files()` which returns a list of changed files compared to upstream.
- `vcs.remote_name` that tracks the name of the remote repository (e.g.: `default` on `hg` or `origin` on `git`)
- `base_ref` parameter that points to the reference (e.g.: a branch) on the base repository
- `vcs.find_latest_common_revision()` which finds the common ancestor between a provided `base_ref` and the current `head_rev`
- `vcs.does_revision_exist_locally()` to find out if a changeset/commit exists in the locally cloned repository
- `base_rev` parameter that points to the most common ancestor between the ancestors of `head_rev` and `base_ref`
- `register_morph` decorator which does what the name implies.

Fixed
- Regression in 2.0.0: action tasks that created new tasks are now green again. ([99](https://github.com/taskcluster/taskgraph/pull/99)/[#100](https://github.com/taskcluster/taskgraph/pull/100))

Changed

- BREAKING CHANGE: `taskgraph.util.taskcluster.status_task` now returns the status object rather than the string state.
- BREAKING CHANGE: Replacement optimization strategies now take a `deadline` argument.
- BREAKING CHANGE: Replaces `Either` base optimization strategy with an `Any` composite strategy.
- BREAKING CHANGE: `taskgraph.util.WHITELISTED_SCHEMA_IDENTIFIERS` is now `taskgraph.util.EXCEPTED_SCHEMA_IDENTIFIERS`.
- BREAKING CHANGE: The `default` target tasks method now filters out tasks that define a `shipping_phase`.

Added
- A new `taskgraph.util.taskcluster.state_task` returns the string state (like status_task used to).
- The ability to register custom optimization strategies.
- Added `release_notifications` transforms, enabling tasks to send e-mail notifications. It is usually
used in the context of releases when you want to inform a group of people about the completion of
a phase of a release. Notifications can contain data about what project/version reached a given
phase.
- New parameters: `version`, `next_version`, `build_number`. As of now, they are be used by
`release_notification` to send e-mails that can contain such data.

Fixed
- Allow JSON-e in schema identifiers

Added
- `run-task` script sets a `TASK_WORKDIR` env pointing to the task specific working directory
- Add `defer` and `enforce_single_match` arguments in `util.schema.resolve_keyed_by`

Fixed
- Misspelling in job transforms causing utility file to be unnecessarily imported
- Added `if-dependencies` to `job_description_schema` allowing it to be used with job transforms

Changed
- Refactored logic for importing sibling modules into new `util.python_path.import_sibling_modules`

Perf
- Skip schema validation when `taskgraph.fast` is set
- Improved performance of `schema.optionally_keyed_by` function

Added
- Support for a `toolchain-env` key which gets added to dependent tasks' environment
- Support for `generic-worker` toolchain tasks
- Ability to execute commands using powershell in `run_task` transforms
- Implicitly run toolchain scripts ending in `.ps1` with powershell

Fixed
- Renaming `toolchain-artifact` now rebuilds toolchain tasks

Fixed
- Git checkout cleaning regression
- Add a mechanism to bypass `--require-hashes` when installing pip dependencies in `run-task`
- Decode gzipped artifacts when using `task-id=` or `project=` in the `--parameters` flag
- Stop defaulting to a dummy `TASKCLUSTER_ROOT_URL` and instead raise error
- Some node dependency upgrades in the `index-task` image