generalize create_climo_files.py

[brianpm]

This changes create_climo_files.py to use adf.data.get_ref_timeseries_file and adf.data.get_timeseries_file to locate the names of the time series files.

This removes the option to provide a custom search string for the time series files, but this could be added to adf.data if needed.

The advantage of this approach is that it means that create_climo_files.py doesn't have to deal with particular history file strings. In cases where the user has supplied a list of history files in the YAML file, the time series generation will loop through the history files, and then create_climo_files.py just finds those time series files. This does mean that if the user provides history file streams that contain the same variable there will be some kind of conflict.

This PR is a step toward being able to include COSP variables back into ADF because currently they have to be written on the CAM native grid (and therefore usually in a separate history stream).