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

@@            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     

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.