[6.19.z] improved rex UI tests reliability

[Satellite-QE]

Cherrypick of PR: #21742

Together with changes to airgun SatelliteQE/airgun#2454 this improves reliability of REX UI tests.

• improved retry on host search page
• re-factored test_positive_run_scheduled_job_template_by_ip
• reusing wait_for results (in some cases there was a wait_for used properly, but then the page was reloaded and search was applied again without wait_for)

Summary by Sourcery

Improve reliability and robustness of remote execution (REX) UI tests by adding resilient host lookup and more deterministic job scheduling assertions.

Bug Fixes:

• Use a retrying wait_for-based host search in REX UI tests to handle delayed host visibility and prevent flaky lookups.
• Stabilize the scheduled job execution test by polling and validating realistic job state transitions before asserting success.

Tests:

• Harden multiple REX UI tests to use shared wait_for results for host searches instead of immediate re-searching.
• Rework the scheduled job-by-IP test to track and assert the sequence of job status transitions through completion.

[Satellite-QE]

trigger: test-robottelo
pytest: tests/foreman/ui/test_remoteexecution.py -k test_positive_run_default_job_template

[Satellite-QE]

PRT Result

Build Number: 16254
Build Status: SUCCESS
PRT Comment: pytest tests/foreman/ui/test_remoteexecution.py -k test_positive_run_default_job_template --external-logging
Test Result : =========== 1 passed, 7 deselected, 9 warnings in 1513.96s (0:25:13) ===========