pants-plugins/uses_services: respect `ST2_DATABASE__*` vars #5534

Job	Run time
Skip Duplicate Jobs Pre Job	4s
Self-check on Python 3.8 - Python 3.8	8m 50s
Lint Checks (black, flake8, etc.) - Python 3.8	2m 53s
Pack Tests - Python 3.8	3m 6s
Compile (pip deps, pylint, etc.) - Python 3.8	4m 6s
Unit Tests (chunk 1) - Python 3.8	7m 4s
Lint Checks (black, flake8, etc.) - Python 3.9	3m 1s
Integration Tests (chunk 1) - Python 3.8	5m 13s
Unit Tests (chunk 2) - Python 3.8	5m 39s
Compile (pip deps, pylint, etc.) - Python 3.9	4m 17s
Integration Tests (chunk 2) - Python 3.8	5m 58s
Unit Tests (chunk 1) - Python 3.9	7m 13s
Pack Tests - Python 3.9	2m 56s
Unit Tests (chunk 2) - Python 3.9	5m 47s
Integration Tests (chunk 1) - Python 3.9	5m 23s
Integration Tests (chunk 2) - Python 3.9	6m 7s
Slack notification for failed master builds	6s
	1h 17m 43s

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