Adding Bucket.lifecycle_rules property to replace methods.

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>

See [RFC (internal only)](https://docs.google.com/document/d/1SNCVTmW6Rtr__u-_V7nsT9PhSzjj1z0P9fAD3YUgRoc/edit#) and https://aip.dev/auth/4111.

Support the self-signed JWT flow for service accounts by passing `default_scopes` and `default_host` in calls to the auth library and `create_channel`. This depends on features exposed in the following PRs: googleapis/python-api-core#134, googleapis/google-auth-library-python#665.

It may be easier to look at https://github.com/googleapis/python-translate/pull/107/files for a diff on a real library.

This change is written so that the library is (temporarily) compatible with older `google-api-core` and `google-auth` versions. Because of this it not possible to reach 100% coverage on a single unit test run. `pytest` runs twice in two of the `nox` sessions.

Miscellaneous changes:
- sprinkled in `__init__.py` files in subdirs of the `test/` directory, as otherwise pytest-cov seems to fail to collect coverage properly in some instances.
- new dependency on `packaging` for Version comparison https://pypi.org/project/packaging/

Co-authored-by: Brent Shaffer <betterbrent@google.com>

🤖 I have created a release \*beep\* \*boop\*
---
## [0.44.0](https://www.github.com/googleapis/gapic-generator-python/compare/v0.43.3...v0.44.0) (2021-04-23)


### Features

* support self-signed JWT flow for service accounts ([#774](https://www.github.com/googleapis/gapic-generator-python/issues/774)) ([89d6f35](https://www.github.com/googleapis/gapic-generator-python/commit/89d6f35c54b0a9b81c9b5f580d2e9eb87352ed93))


### Bug Fixes

* enable GAPIC metadata generation ([#843](https://www.github.com/googleapis/gapic-generator-python/issues/843)) ([697816c](https://www.github.com/googleapis/gapic-generator-python/commit/697816ce7d5b201d6ced85fadd89f9140da67b37))
---


This PR was generated with [Release Please](https://github.com/googleapis/release-please). See [documentation](https://github.com/googleapis/release-please#release-please).

…fig (#774)

Source-Link: googleapis/synthtool@106d292
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Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

* chore: expand Target.target_id docs
chore: improve FieldReference.field_path docs
chore: (preview only) expose Query Profile API

PiperOrigin-RevId: 570489360

Source-Link: googleapis/googleapis@5c5f6b7

Source-Link: googleapis/googleapis-gen@cb29ed5
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* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

---------

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>

Source-Link: googleapis/synthtool@1b71c10
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-python:latest@sha256:00c9d764fd1cd56265f12a5ef4b99a0c9e87cf261018099141e2ca5158890416

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

…774)

* feat: Add ListDatabaseRoles API to support role based access control

PiperOrigin-RevId: 462086058

Source-Link: googleapis/googleapis@4f072bf

Source-Link: googleapis/googleapis-gen@06f699d
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* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>