Add diagnostic metadata property to constituents object; use existing diagnostic name metadata attribute

[peverwhee]

Add diagnostic_name to the constituent properties object and enable setting via instantiate calls and metadata attributes.

Includes:

• Mods to src/ccpp_constituent_prop_mod.F90 to add the var_diag_name property and set it via instantiate. Also includes methods to retrieve the diagnostic name for a given constituent.
• Mods to scripts/metadata.py and scripts/var_props.py to include a default diagnostic name (set to local name)
• Mods to the advection test to confirm the new diagnostic name property is set correctly (and defaults correctly) for both run-time and build-time constituents

User interface changes?: Yes - all calls to %instantiate (dynamic, run-time constituents created during the register phase) must now include the diagnostic name in the argument list. This only impacts CAM-SIMA right now because that's the only host model using the dynamic constituents, to my knowledge.

closes #635

[dustinswales]

These changes look fine to me.
At the moment I don't see a use case for them on the NOAA side, but the added functionality doesn't hurt.

[gold2718]

I'm not sure what to say about this. This seems mostly fine (see minor request) but I think you have implemented the diagnostic_name_fixed property. I think we need to just revisit these properties and decide what we will want in the future.

[gold2718]

Is this necessary?
From https://docs.python.org/3/library/stdtypes.html#text-sequence-type-str
"The slice of s from i to j is defined as the sequence of items with index k such that i <= k < j. If i or j is greater than len(s), use len(s)."

Suggested change

	maxlen = 256
	diag_name = stdname[:maxlen] if len(stdname) > maxlen else stdname
	maxlen = 256
	diag_name = stdname[:maxlen]

[mkavulich]

@peverwhee Do you have an answer to this question?

[peverwhee]

yes sorry for the delay! I've pushed up @gold2718 's suggested change

[mkavulich]

@climbfuji This PR needs a review from the NEPTUNE side

[climbfuji]

I don't know a lot about this part of the code but from what I understand it makes sense. Please address @gold2718's question/comment before merging.

[mkavulich]

@peverwhee Just checking in on the status of this PR. It'll need updating to the top of develop, and addressing Steve's latest question.

[peverwhee]

thanks for the ping, @mkavulich !

I've re-requested @gold2718 's review