Introduce init_pio_mod with the initialization pieces from shr_pio_mod

[billsacks]

This PR introduces an init_pio_mod that contains just the initialization pieces from shr_pio_mod (from the share repository).

This is part of a set of changes where I am splitting shr_pio_mod into two pieces:

(1) Reading configuration files and initializing PIO appropriately

(2) Storing information about PIO (io system descriptors, io types, io formats) and providing an interface to query this information

Piece (2) lives in the share code and is used regardless of the driver. Piece (1) is driver-specific, so for now we have three versions of that piece: one in CMEPS (created by extracting the initialization pieces from cmeps/cesm/nuopc_cap_share/shr_pio_mod.F90), one in the cpl7 repo (created by extracting the initialization pieces from share/src/shr_pio_mod.F90), and one in CTSM's LILAC directory (which is essentially identical to the one in the cpl7 repo). Piece (2) – the actual share code piece – is used by components (their use statements stay exactly as they are now) as well as by piece (1) (which is responsible for setting the module-level variables in piece (2)).

See ESCOMP/CTSM#1759 (comment) for more context.

Needs to be coordinated with ESCOMP/CESM_share#34 . See also the related PR for CMEPS: ESCOMP/CMEPS#306

[jedwards4b]

I wonder if driver_pio would be better than init_pio? So
driver_pio_init1, driver_pio_init2, driver_pio_finalize instead of the awkward
init_pio_init1 and init_pio_finalize?

[billsacks]

I wonder if driver_pio would be better than init_pio?

Sounds good. I'll make this change in the relevant places.

I see that SRT is failing. I think it's because it's grabbing the latest master branch from dependent repos rather than grabbing the interdependent branches. Do you have suggestions for how to handle this? (Or do we just let SRT fail here?)

[jedwards4b]

I would say just run srt locally and make sure it passes.

[billsacks]

I would say just run srt locally and make sure it passes.

I'm trying to figure out how to do this. Is the procedure documented somewhere? I think I can see how to do this from a cime-centric standpoint: get the latest cime, run checkout_externals to get the various externals set up, then change the versions of externals, then run 'pytest -vvv' from the top-level cime directory. Is that how you would do this, or is there a better method for running srt locally on these various repositories?

[billsacks]

Actually, I'm having trouble getting pytest -vvv off the ground on cheyenne. I think I need some step-by-step instructions for dummies, including how to get the environment (python version, etc.) set up appropriately for this now.

[billsacks]

I have run CESM prealpha testing on these changes. All tests pass other than those that failed in the baseline as well. @jedwards4b let me know if you'd like me to do any other testing – and if you'd like me to do the srt testing by hand, please help me with exactly how to do that.