Fix more rubocop warnings

[jay7x]

No description provided.

[jay7x]

To be rebased and merged after #106

[codecov]

Codecov Report

Patch coverage: 66.66% and project coverage change: -0.15 ⚠️

Comparison is base (135b8fe) 85.61% compared to head (57fcbeb) 85.46%.

❗ Current head 57fcbeb differs from pull request most recent head b5c3b8f. Consider uploading reports for the commit b5c3b8f to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #108      +/-   ##
==========================================
- Coverage   85.61%   85.46%   -0.15%     
==========================================
  Files           1        1              
  Lines         292      289       -3     
==========================================
- Hits          250      247       -3     
  Misses         42       42              

Impacted Files	Coverage Δ
lib/beaker/hypervisor/docker.rb	85.46% <66.66%> (-0.15%)	⬇️

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