use cesm logging facilities

[jedwards4b]

This modification redirects FMS library logging to the cesm log files without requiring any changes in the
FMS src repository. A note of caution - if an update of FMS updates the source of any file which is copied in
the src_override directory then CESM developers must merge those updates by hand into the files in src_override.

[alperaltuntas]

@jedwards4b , Have you tested this srcmod with both MOM6 and FV3? When both models are active, which log file do the FMS logs go to?

Could you describe the necessary changes you applied, so as to guide the efforts to port these changes in the future. When compared with 2020.04.03, it looks like you removed bunch of empty lines, which is confusing. I guess it is not necessary to repeat the removal of those lines in a future port.

Also, FV3 folks should also chime in on this PR. @jtruesdal

PS :@jtruesdal and I talked about bumping up the FMS version to 2021.03.01 earlier this year. So just a heads up that this srcmod may have to be ported to 2021.03.01 soon. (MOM6 is ready for 2021.03.01, but I am not sure if FV3 is yet.)

[jedwards4b]

Hi @alperaltuntas, we do not currently have a working fv3 so it's difficult to test, but the calls to shr_log_setLogUnit in the component cap controls the unit where subsequent writes will happen. So when the mom component is active fms output will go to the ocn.log and when the fv3 component is active they will go to the atm.log. I will assure this is the case when we are able to run both together. I'm not sure I understand your comment about comparing to 2020.04.03, I don't see any empty lines in the diff.