FV nudging module contains endrun calls without messages

A recent DiscussCESM [forum post](https://bb.cgd.ucar.edu/cesm/threads/case-run-error.6118/#post-40099) presented a situation where a user was getting confused due to the lack of any sort of abort message for an `endrun` call in `src/dynamics/fv/metdata.F90`, which is used for specified-dynamics nudging runs. Upon further examination there are several other `endrun` calls in this module that are also missing any sort of error message.

Thus to avoid user confusion in the future, it would be good to add actual error messages to the `endrun` calls in that module.