ATMRES getting reset in export_cpl()

[dpsarmie]

Description

There is an export call in default_vars.sh export_cpl() that resets ATMRES. Most of the regression tests still reset relevant parameters so they are unchanged but this should be changed since it will have unforeseen consequences in future tests.

To Reproduce/Fix:

default_vars.sh will be changed to keep ATMRES/ICERES/OCNRES unchanged if it is already set. ATMRES check will be done in export_fv3() while the ICERES and OCNRES checks will be in export_cpl().