Build python virtual environments.

[aerorahul]

This PR:

• adds ability to build python virtual environments and load them as modules. This is a desired functionality for users of applications that require different combinations of python packages.
• This functionality is currently being exercised in JEDI related projects such as EWOK, JEDI-GDAS HofX applications.
• This functionality can be leveraged for other applications requiring python virtual environments e.g. JEDI-SOCA, MetPlus, etc.

To load a python virtual env. is the same as loading any other library or utility. Loading the module will place the user in the python virtual env. (akin to source venv/bin/activate). Unloading deactivate's the virtual environment.

Also in this PR,

• the yaml files have been moved to stack/ from config/
• virtual environment requirements.txt files will be placed under pyvenv/
• Updates to README.md on how to add a virtual environment and correct paths for JEDI dependencies

[aerorahul]

@kgerheiser
Can I please get a review on this?

[kgerheiser]

Are the JEDI repositories private? I tried building r2d2, but it asks for a Github password.

[aerorahul]

Yes. They are private at the moment and hence the build is turned OFF.

[aerorahul]

thanks @kgerheiser

[edwardhartnett]

We are going to move from hpc-stack to spack for distributing our libraries. How will this capability be transitioned?

[aerorahul]

That is for you to figure out.

[climbfuji]

We are going to move from hpc-stack to spack for distributing our libraries. How will this capability be transitioned?

I am surprised to hear that the decision to move to spack was already made, but maybe I misunderstood the discussion yesterday. I think it is a good approach, but it needs more testing (we have roadmap for it) and it's not set in stone yet. Whatever we agree on, there'll be a lot of things that need to be transitioned (by someone).