RuboCop: fix layout cops, disable GuardClause; fix license in gemspec

[bastelfreak]

cherry-picked some of the changes from #291

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (734050d) 0.66% compared to head (4cd9914) 0.66%.

❗ Current head 4cd9914 differs from pull request most recent head c03196b. Consider uploading reports for the commit c03196b to get more accurate results

Additional details and impacted files

@@          Coverage Diff           @@
##           master    #306   +/-   ##
======================================
  Coverage    0.66%   0.66%           
======================================
  Files          15      15           
  Lines        1954    1953    -1     
======================================
  Hits           13      13           
+ Misses       1941    1940    -1     

Impacted Files	Coverage Δ
lib/beaker-hostgenerator/cli.rb	0.00% <0.00%> (ø)
lib/beaker-hostgenerator/data.rb	0.00% <0.00%> (ø)
lib/beaker-hostgenerator/hypervisor/hcloud.rb	0.00% <0.00%> (ø)
lib/beaker-hostgenerator/parser.rb	0.00% <0.00%> (ø)
lib/beaker-hostgenerator/roles.rb	0.00% <0.00%> (ø)
test/util/generator_helpers.rb	27.08% <ø> (ø)

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