Dsub

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`.

This release includes:
- `dsub`
- (New) (Experimental) Implemented google-cls-v2 provider that passes all tests.
- Pin all dsub dependencies to a max version
- Fix broken urls in dsub docs.
- Add dsub --summary output in wait_and_retry loop.
- `google-v2` provider updates:
- Enable a shared PID namespace when `--ssh` is specified.
- Also retry broken pipe errors
- Setting `--preemptible 0` should not cause an error.
- Testing
- Change Travis Python3 version from 3.8 to 3.7.
- Remove sorting_util_test.

This release includes:

- `dsub`
- Add periodic status update in output (via `--summary` flag).
- Update help text to clarify that `timeout` has a default of 7 days.
- Replace apiclient with googleapiclient.
- Emit a message to make it more clear that the dsub process must continue running for retries.
- Add missing quotes in documentation in example for `--mount`.
- `google-v2` provider updates:
- Update gsutil rsync warning message to include command being run.
- Add workaround for gsutil/gcloud bug that prevents re-authentication.

This release includes:

- `dsub`
- Fix RFC3339 date parsing errors with specific values under Python3
- `google-v2` provider updates:
- Filter out warning from `google-auth`.
- Retry `ResponseNotReady` error.
- Add zones for Zurich and Osaka.
- Move "sleep before retry" messages from `INFO` in stdout to `WARNING` in stderr. This ensures that the retry messages bubble up to the stderr output recorded in the pipeline's operation.