Add support for RHEL instances in AWS

[tophercullen]

AWS instances have a different repo structure and cannot be managed
with the subscription manager utils

[coderanger]

Yeah, RedHat had promised me they would work out a better way to do this but that was like a year ago and nothing has happened so sighhhh. This probably won't work on other RedHat cloud images for the same reasons but I can only fix so much. This is a start but the eventual fix is probably going to be 1) default to IUS instead of SCL and 2) within the scl provider default to using the CentOS recompiles even on RHEL unless specifically configured to use the official repos.

[codecov-io]

Codecov Report

Merging #9 into master will decrease coverage by 0.86%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master       #9      +/-   ##
==========================================
- Coverage   98.22%   97.36%   -0.87%     
==========================================
  Files          14       14              
  Lines         451      455       +4     
==========================================
  Hits          443      443              
- Misses          8       12       +4

Impacted Files	Coverage Δ
lib/poise_languages/scl/resource.rb	88.88% <0%> (-6.03%)	⬇️

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[tophercullen]

@coderanger I'm not familiar with codecov, Is there something else I need to add to the PR?