Errata WIP for remaining UI Failures

[damoore044]

Problem Statement

Fix remaining UI errata failures (8-10 in recent CI 6.15.0/stream)

• Fixture improvements
• Remove some remaining outdated setup/ unusable fixtures
• Fix intermittent failures of test_end_to_end and _pagination
• Makes use of api_factory method proposed (in-review) #14974

Ongoing Failures

• test_positive_content_host_previous_env: Skipped for now, until BZ #2280882 is resolved.
• test_positive_apply_for_all_hosts: Testing local fix, Airgun PR #1387

PRT Case

trigger: test-robottelo
pytest: tests/foreman/ui/test_errata.py
airgun: 1387