* Remove default use of paramiko connection plugin on macOS
This fix was originally to work around a bug that caused a kernel panic on macOS
that has since been fixed.
* Remove paramiko from requirements.txt
* Move paramiko checking to common place
* Drop the warnings obfiscation code
* Update pip installation instructions to reflect upstream instructions
* Fix tests on CentOS 6 (Python 2.6) that now show Python deprecation warnings
* Add changelog fragment
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