Enhance documentation about roles

[rwaffen]

if one does not set any role, you get an error

     Failure/Error: it { is_expected.to be_installed }
     Beaker::DSL::Outcomes::FailTest:
       There should be one host with default defined!

One and only one is allowed to be default.

Failure/Error: configure_beaker
ArgumentError:
  Only one host may have the role 'default', default roles assigned to [:"ubuntu-20-04", :"ubuntu-18-04", :"ubuntu-22-04"]

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (c00e1be) 74.65% compared to head (c2caef8) 74.65%.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1800   +/-   ##
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  Coverage   74.65%   74.65%           
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  Files          81       81           
  Lines        4494     4494           
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  Hits         3355     3355           
  Misses       1139     1139           

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[ekohl]

I think this isn't exactly true. AFAIK roles are mandatory on multi-host setups, but optional on single host setups.

[rwaffen]

ah okay. makes sense. in my single host setup it worked until i changed it to multihost. then i try to put this somehow into a sentence. 🤔

[bastelfreak]

@rwaffen please rebase to get rid of the merge commit.