Different adjustments and improvements across the board

[amotl]

• Assign Vagrant environment more resources (4 VCPUs and 4096 MB RAM).
• Add platform guards: Protect specific subsystems from being executed on unknown operating systems..
• Improve central command invocation function.
• Improve documentation.
• Set the stage for Make Windows runner subsystem production ready #4.

[codecov-commenter]

Codecov Report

Merging #3 (d21208f) into main (334b28b) will decrease coverage by 0.26%.
The diff coverage is 68.42%.

@@            Coverage Diff             @@
##             main       #3      +/-   ##
==========================================
- Coverage   82.53%   82.26%   -0.27%     
==========================================
  Files          18       18              
  Lines        1145     1156      +11     
==========================================
+ Hits          945      951       +6     
- Misses        200      205       +5     

Flag	Coverage Δ
unittests	82.26% <68.42%> (-0.27%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
racker/cli.py	86.07% <ø> (-0.35%)	⬇️
postroj/util.py	75.54% <66.66%> (-0.71%)	⬇️
postroj/pkgprobe.py	89.04% <75.00%> (-0.96%)	⬇️

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