Ensure HEAD requests on port 80 can actually go through, including timeout checks (only used by the Opossum test at the moment, fixes #2847)

[GottemHams]

Describe your changes

See #2847 for more details.

What is your pull request about?

• Bug fix
• Improvement
• New feature (adds functionality)
• Breaking change (bug fix, feature or improvement that would cause existing functionality to not work as expected)
• Typo fix
• Documentation update
• Update of other files

If it's a code change please check the boxes which are applicable

• For the main program: My edits contain no tabs, indentation is five spaces and any line endings do not contain any blank chars
• I've read CONTRIBUTING.md and Coding_Convention.md
• I have tested this fix or improvement against >=2 hosts and I couldn't spot a problem
• I have tested this new feature against >=2 hosts which show this feature and >=2 host which does not (in order to avoid side effects) . I couldn't spot a problem
• For the new feature I have made corresponding changes to the documentation and / or to help()
• If it's a bigger change: I added myself to CREDITS.md (alphabetical order) and the change to CHANGELOG.md

[drwetter]

Thanks a lot for your work, @GottemHams ! I prefer my PR going forward.

Just needs to be tested for cases which doesn't have port 80 opened. And it's a matter of balancing that with when does a block happen there. For the latter and atm I'd tend to not put it into the background. If somebody has good arguments otherwise, I am all ears.