Add redis user and password support

[abulte]

• I've added tests to cover the proposed changes

Changes proposed in this pull request:

• add support for Redis authentification through DPP_REDIS_USERNAME and DPP_REDIS_PASSWORD env vars

Replaces #199

[coveralls]

Pull Request Test Coverage Report for Build 1168

• 6 of 9 (66.67%) changed or added relevant lines in 3 files are covered.
• 80 unchanged lines in 6 files lost coverage.
• Overall coverage decreased (-8.5%) to 17.103%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
datapackage_pipelines/status/backend_redis.py	1	2	50.0%
datapackage_pipelines/celery_tasks/dependency_manager.py	0	2	0.0%

Files with Coverage Reduction	New Missed Lines	%
.tox/py37-plyvel/lib/python3.7/site-packages/datapackage_pipelines/status/backend_redis.py	10	0%
.tox/py37-sqlite/lib/python3.7/site-packages/datapackage_pipelines/status/backend_redis.py	10	0%
.tox/py37-plyvel/lib/python3.7/site-packages/datapackage_pipelines/status/status_manager.py	14	0%
.tox/py37-sqlite/lib/python3.7/site-packages/datapackage_pipelines/status/status_manager.py	14	0%
.tox/py37-plyvel/lib/python3.7/site-packages/datapackage_pipelines/celery_tasks/dependency_manager.py	16	0%
.tox/py37-sqlite/lib/python3.7/site-packages/datapackage_pipelines/celery_tasks/dependency_manager.py	16	0%

Totals
Change from base Build 1166:	-8.5%
Covered Lines:	1739
Relevant Lines:	10168

---

💛 - Coveralls