Use timecop to lock date to 20200312 for certs

What does this MR do?

Uses timecop to lock date in for pages_domain related tests due to test-certifcate expiration date on 2020-04-12 causing date dependent failures.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Closes #210557 (closed)