Chaostoolkit

Changed

- Fixed `--var` and `--var-file` arguments parsing by addition of missing
return into `validate_vars` function

Changed

- Remove Python 3.5 support. [Requires 3.6][208] at least now until end of 2021
when [Python 3.6 reaches EOL][pyeol].

[pyeol]: https://devguide.python.org/#status-of-python-branches
[208]: https://github.com/chaostoolkit/chaostoolkit/issues/208

**LAST VERSION SUPPORTING PYTHON 3.5**

Changed

- Updated build scripts to support latest setuptools to build package properly

Changed

- Updated pyyaml to due to CVE-2020-14343 [206][206]
- Pinning Chaos Toolkit lib to strictly less than 1.19.0 as it'll be the last
one supporting Python 3.5 [194][194]
- Moved to setup.cfg to manage build

[206]: https://github.com/chaostoolkit/chaostoolkit/issues/206
[194]: https://github.com/chaostoolkit/chaostoolkit/issues/194

Changed

- Pass extra variables down to the runner for substitution
[chaostoolkit-lib192][ctklib192]

[ctklib192]: https://github.com/chaostoolkit/chaostoolkit-lib/issues/192

Added

* Add the `--hypothesis-strategy` flag to the `run` command. It defines how the
steady-state hypothesis is applied. One of:
* `default` is the classic mode where the hypothesis is run before and after
the method
* `before-method-only` runs the hypothesis once only before the method
* `after-method-only` runs the hypothesis once only after the method. This is
useful when you know your environment is not in the appropriate state
before the conditions are applied
* `during-method-only` runs the hypothesis repeatedly during the method but
not before nor after
* `continously` runs the hypothesis repeatedly during the method as well as
before and after as usual
* Add the `--hypothesis-frequency` flag to the `run` command. This flag is
only meaningful with `--hypothesis-strategy=during-method-only|continously`.
It takes a floating number indicating how many seconds to wait between two
executions of the hypothesis
* Add the `--fail-fast` flag to the `run` command. This flag is
only meaningful with `--hypothesis-strategy=during-method-only|continously`.
If set, this indicates the experiment should be marked as deviating
immediately. When not provided, the hypothesis runs until the end of the
method without terminating the experiment

Changed

- Bump dependency on chaostoolkit-lib to 1.13.0 to support the steady state
strategy