Sync task-standard (#26)

Project import generated by Copybara.

Co-authored-by: Task Standard Authors <[email protected]>

0.2.3 (#15)

0.2.2 (#12)

- Support custom code for task environment teardown
- Support `p3` AWS instances
- Fix a bug where the workbench fails to set up `iptables` rules for
task environments unless it's explicitly given root access on the
machine running Docker. The fix is to have the workbench ask for root
access using `sudo`
- Other bugfixes and formatting

0.2.1

0.2.0

0.1.1