* Make sure ruamel.yaml.clib 0.2.2 is used for Python 2.7.
* Also add to unit tests requirements.
* Don't install on Python 2.6.
* Another constraints file.
* Limit cryptography to < 3.4 for Python < 3.6.
* Work around old pip versions.
* Use constraints file when installing stormssh.
* Work around old pip in RHEL8.2, CentOS 8, Ubuntu 18.04, and OpenSuSE 15
(cherry picked from commit 909ac92fe2)
* Work around old pip versions which install yanked packages.
* Try II
* Proper approach.
* Avoid too old version being installed.
(cherry picked from commit 38996b7544)
Co-authored-by: Felix Fontein <felix@fontein.de>