Dsub

Release `0.4.2` of `dsub` ends support Python 3.5, which [reached its "end of life" at the end of September, 2020](https://www.python.org/downloads/release/python-3510/#:~:text=Python%203.5%20will%20reach%20its,release%20of%20the%203.5%20series.).

The last version of `dsub` that supports Python 3.5 is 0.4.1.
Please use Python 3.6 or greater.

This release includes:

- Python code health
- Remove uses of `future` from `dsub`
- Remove `six` and its usages from `dsub`
- Explicitly support Python 3.6 and up.
- Feature updates
- Improvements to `dstat` output
- Use "tenacity" library instead of "retrying" library for API retries.
- Add a get_credentials function that Python clients of `dsub`, `dstat`, `ddel` can override for non-standard runtime environments.
- `google-cls-v2` provider updates:
- Use batch endpoint in `google-cls-v2` provider for job deletion (`ddel`).
- google-cls-v2: Use the batch endpoint only for `--location us-central1`.

This release includes one change to support users of Python 3.5:

- Remove a use of [f-string](https://www.python.org/dev/peps/pep-0498/)s, which was introduced in Python 3.6.

Release `0.4.0` completes the sunsetting of Python 2 support for `dsub`.
The last version of `dsub` that supports Python 2 is `0.3.10`.

This release also adds a WARNING when the `--image` flag is omitted from a call to `dsub`.
The default image is available as a getting started convenience, but for ongoing reproducible workflows, the image should be specified by the caller.
The current default is `ubuntu:14.04` which reached [End Of Life in April 2019](https://wiki.ubuntu.com/Releases). The default image will change in future releases and it is likely to be changed on a semi-regular basis, as popular base Docker linux images change.

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This release includes:
- dsub
- Update setup.py in dsub to be Python 3 only.
- Lint dsub source files as Python3 only. Fix a few lint warnings.
- Emit warning if default image is used.
- Print full path of exceptions that are retried.
- Print retry errors for socket timeout error.
- Add socket.timeout exceptions to the retry list.
- Fix markdown formatting in `dsub` README

This release includes:

- `dsub`
- Update Makefile to use Python3 venv
- Add documentation around Compute Engine Quotas.
- Have `dsub` output job-name and user-id in addition to job-id prior to launching job.
- Fix for `--users '*'`
- Update `httplib2` for `dsub` to 0.18.1
- Retry transient http error codes when checking GCS
- Fix for yaml 5.3 where timestamps are already loaded as timezone aware.
- Improve performance of GCS output file checks for `--skip`

This release includes:

- `dsub`
- Update version of cloudsdk docker image and revert workaround for `gsutil`/`gcloud` auth token bug on GCE, which should now be fixed in the updated image.
- Update `google-auth` to 1.18.0 and pin `google-api-core` to 1.21.0
- Remove leading characters that are not a letter, number, or underscore when auto-creating a `job-name` from a command string.
- Move `google_v2` arguments to `google_common` in the `--help` text.
- Add a section in the documentation for Google provider-specific command-line flags.
- Remove support/tests for legacy `local` provider job metadata file
- Testing updates:
- Re-enable the test `e2e_errors.sh` for all providers.
- Add unit test for retrying BrokenPipeError
- Fix ResourceWarning when running python unit tests.

This release includes:
- `dsub`
- Remove the `google` provider and its documentation.
- Document the existence of the `google-cls-v2` provider
- Document using `venv` for installation
- Add a flag `--credentials-file` to pass service account credentials to the provider.
- `google-v2` provider updates:
- Add `--ssh` to dstat.
- `google-cls-v2` provider updates:
- Add default locations for `google-cls-v2` in `dstat` and `ddel`.