(GH-896) Support beaker testing on windows server 2012r2 (continued)

[treydock]

This is a continuation of #897

$ bundle exec rake beaker:windows-server-2012r2
<SNIP>
Finished in 2 minutes 42 seconds (files took 5 minutes 44 seconds to load)
13 examples, 0 failures, 7 pending

Could probably use unless with contexts that should skip for windows but wasn't sure if better to have output explaining why some tests were skipped or just skip silently.

[ghoneycutt]

Released in v2.53.0