[6.15.z] [stream] fixes for combined session failures, Errata UI

[Satellite-QE]

Cherrypick of PR: #14822

Problem Statement

Initial PR #14773 raised by @LadislavVasina1, for 3 errata UI test fixes/updates.

• troubleshoot PRT failures in combined session, running the 3 tests from above PR.

Error in setup for test_positive_check_errata_counts_by_type_on_host_details_page :

Locally have intermittently reproduced issue with the registered_contenthost UI fixture with adding repos to cv, and promotion of cv to lce, in between parameters of combined session. Issues with some associated activation keys not being deleted in cleanup.

^^ Issues fixed with 2nd commit.

PRT Case

trigger: test-robottelo
pytest: tests/foreman/ui/test_errata.py -k 'test_positive_check_errata or test_positive_errata_search_type or test_positive_check_errata_counts_by_type_on_host_details_page or test_positive_list and not test_positive_list_permission'

• We run the 3 impacted tests from @LadislavVasina1 's PR and commits,
  along with test_positive_list, which fails in CI and is fixed by the changes.
  We exclude the otherwise collected test_positive_list_permissions, it is not impacted by these changes.

[Satellite-QE]

trigger: test-robottelo
pytest: tests/foreman/ui/test_errata.py -k 'test_positive_check_errata or test_positive_errata_search_type or test_positive_check_errata_counts_by_type_on_host_details_page or test_positive_list and not test_positive_list_permission'

[Satellite-QE]

PRT Result

Build Number: 6758
Build Status: SUCCESS
PRT Comment: pytest tests/foreman/ui/test_errata.py -k test_positive_check_errata or test_positive_errata_search_type or test_positive_check_errata_counts_by_type_on_host_details_page or test_positive_list and not test_positive_list_permission --external-logging
Test Result : ========= 4 passed, 12 deselected, 171 warnings in 1342.43s (0:22:22) ==========