Switch test runner from nosetest to pytest #5619

Job	Run time
Skip Duplicate Jobs Pre Job	5s
Lint Checks (black, flake8, etc.) - Python 3.8	2m 40s
Pack Tests - Python 3.8	2m 57s
Compile (pip deps, pylint, etc.) - Python 3.8	3m 43s
Self-check on Python 3.8 - Python 3.8	8m 26s
Integration Tests - Python 3.8	9m 10s
Lint Checks (black, flake8, etc.) - Python 3.9	3m 4s
Unit Tests - Python 3.8	16m 12s
Pack Tests - Python 3.9	2m 48s
Unit Tests - Python 3.9	16m 36s
Compile (pip deps, pylint, etc.) - Python 3.9	4m 13s
Integration Tests - Python 3.9	9m 29s
Slack notification for failed master builds	5s
	1h 19m 28s

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