tests: Always set the platform as a Beaker::Platform instance

[ekohl]

In Beaker 4.39.0 it uses the platform.variant method. Previously it stubbed .to_array, but that is no longer sufficient. This changes the tests to use an actual Beaker::Platform instance rather than a mock Object.

Fixes voxpupuli/beaker#1772

[codecov]

Codecov Report

Base: 78.19% // Head: 78.19% // No change to project coverage 👍

Coverage data is based on head (656b92a) compared to base (94be176).
Patch coverage: 71.42% of modified lines in pull request are covered.

❗ Current head 656b92a differs from pull request most recent head 708ad54. Consider uploading reports for the commit 708ad54 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #209   +/-   ##
=======================================
  Coverage   78.19%   78.19%           
=======================================
  Files          15       15           
  Lines        1605     1605           
=======================================
  Hits         1255     1255           
  Misses        350      350           

Impacted Files	Coverage Δ
lib/beaker-puppet/helpers/puppet_helpers.rb	86.49% <0.00%> (ø)
lib/beaker-puppet/install_utils/foss_utils.rb	70.12% <83.33%> (ø)

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