fix failing build on hosts with wildcard dns (fixes #1230)

[neolynx]

Replaces #1231

on hosts which have wildcard dns domains in their local domain search list, builds failed because "nosuch.host" could actually be resolved.

Since ".host" isn't a recommended TLD by RFC2606, we use ".invalid" now. And since this is not enough to fix the problem, we use now absoulte domain names (having a '.' at the end)

Fixes #1230

Requirements

All new code should be covered with tests, documentation should be updated. CI should pass.

Description of the Change

Checklist

• [ ] unit-test added (if change is algorithm)
• [ ] functional test added/updated (if change is functional)
• [ ] man page updated (if applicable)
• [ ] bash completion updated (if applicable)
• [ ] documentation updated
• [ ] author name in AUTHORS

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 74.81%. Comparing base (8d09c20) to head (e6585c6). Report is 1 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1278 +/- ## ========================================== + Coverage 74.79% 74.81% +0.02% ========================================== Files 144 144 Lines 16256 16248 -8 ========================================== - Hits 12158 12156 -2 + Misses 3156 3152 -4 + Partials 942 940 -2 ```

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