Centralize pyenv install logic

[pavera]

Context

As part of the work to allow Dependabot to work reliably when isolated from the internet some code cleanup has been identified. This is the beginning of the work to limit the places where we make attempts to talk to the public internet

Approach

I've added a new helpers.rb for python which will contain various methods which are currently copy/pasted between the various python package manager implementations. The first method I've moved over is the method that installs new python versions via pyenv install.

Ongoing

I am pretty sure the python_version and the methods it calls in the various implementations can also be moved to the new helpers.rb and I will be working on that next.

[honeyankit]

Looks good to me

[pavera]

@mctofu will this log as you are expecting to allow us to search in a central place?