[GH-1322] Detect broken yum install python-requests

[c-w]

Detect issues with libcloud and python-requests on RHEL 7

Description

As discussed in #1322, libcloud breaks when used on RHEL 7.6 with requests installed from yum instead of PyPI. In order to prevent user confusion, this pull request introduces a check for this environment state and provides guidance for the user on how to correctly set up their system for libcloud to function.

Resolves #1322

Status

• done, ready for review

Checklist (tick everything that applies)

• Code linting (build passed)
• Documentation (updated changelog)
• Tests (added unit test)
• ICLA (required for bigger changes)

[codecov-io]

Codecov Report

Merging #1332 into trunk will decrease coverage by <.01%.
The diff coverage is 90%.

@@            Coverage Diff             @@
##            trunk    #1332      +/-   ##
==========================================
- Coverage   86.34%   86.34%   -0.01%     
==========================================
  Files         372      372              
  Lines       75825    75845      +20     
  Branches     6928     6929       +1     
==========================================
+ Hits        65473    65489      +16     
- Misses       7569     7572       +3     
- Partials     2783     2784       +1

Impacted Files	Coverage Δ
libcloud/compute/drivers/gce.py	76.84% <100%> (+0.01%)	⬆️
libcloud/test/compute/test_gce.py	97.77% <100%> (ø)	⬆️
libcloud/test/test_init.py	85.29% <100%> (+4.52%)	⬆️
libcloud/__init__.py	67.64% <75%> (+2.26%)	⬆️
libcloud/test/compute/test_upcloud.py	90.06% <0%> (-1.33%)	⬇️

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[Kami]

Can you please also add a test case for it?

On a related note - we should also advise uses to use virtualenv with no system packages in such scenario (that's a good practice in general).

[c-w]

@Kami I believe I addressed all the comments. I also verified that python setup.py install works on a clean virtualenv. Could you please take another look and let me know if this is ready for merge? Thanks!

[Kami]

Sorry for the delay. I pushed a small change (8d179ed), besides that it looks good to me 👍

[Kami]

@c-w a lot of changes have accumulated in trunk since the last release.

Do you want to start the work needed to get the 2.6.0 release out - https://libcloud.readthedocs.io/en/latest/committer_guide.html#making-a-release-for-release-managers?