Add initialization of n_aero to icepack driver

[apcraig]

PR checklist

• Short (1 sentence) summary of your PR:
  Add initialization of n_aero in icepack driver
• Developer(s):
  apcraig
• Suggest PR reviewers from list in the column to the right.
• Please copy the PR test results link or provide a summary of testing completed below.
  Tested in icepack on conrad with 4 compilers. All tests pass EXCEPT the pondcesm test case indicates non-bit-for-bit vs the baseline. I have compared the ice_diag files for all pondcesm cases vs the baseline, and they are bit-for-bit, but the restart file (which is what is compared in the test) is not. I suspect something is written slightly different into the restart file that does not affect answers. This seems to happen just for the pondcesm case. I don't understand why. Because the restart files are binary, it's not easy to identify the differences. But I think we can accept this since the ice_diag files are identical.
  https://github.com/CICE-Consortium/Test-Results/wiki/icepack_by_hash_forks#7259556232cebf37f4c9b42b4ba0b866a07d196b
• How much do the PR code changes differ from the unmodified code?
  • bit for bit
  • different at roundoff level
  • more substantial
• Does this PR create or have dependencies on CICE or any other models?
  • Yes
  • No
• Does this PR add any new test cases?
  • Yes
  • No
• Is the documentation being updated? ("Documentation" includes information on the wiki or in the .rst files from doc/source/, which are used to create the online technical docs at https://readthedocs.org/projects/cice-consortium-cice/.)
  • Yes
  • No, does the documentation need to be updated at a later time?
    • Yes
    • No
• Please provide any additional information or relevant details below:

[dabail10]

This looks fine. I am wondering though if we need a call to get n_aero_out as well? I'm not sure I understand how these different in/out variables are used.

[apcraig]

Thanks @dabail10 and @eclare108213. In general, the values have to be set within the columnphysics part of icepack thru the icepack interfaces. How any driver handles management in the driver is up to the driver. You can store the variable in the driver and reuse them there or you can query icepack to get the value. That is not specified. The main issue is that things need to be set in the columnphysics part of icepack and you cannot access that data via a "use" statement.

I will merge the PR now and then it can be included in weekend testing. Thanks!