Generalize the mosiac file name that chgres_cube can read in.

[gsketefian]

This PR allows chgres_cube to read in a mosaic file with a name that has any separator character (not just an underscore) between the starting $CRES and the string "mosaic" that follows $CRES. For example, this will allow the mosaic file to be named C768.mosaic.halo4.nc instead of C768_mosaic.halo4.nc (note the "." instead of the "_" after "C768").

This is to allow the regional_workflow to use fixed file names for the grid and orography files that have the same naming convention as the fixed surface climo files that the sfc_climo_gen code generates. That convention is to use a "." between the $CRES and the string "mosaic" instead of an underscore.

This was tested in the regional_workflow and works both for the case of an "_" and a "." as the separator character in the mosaic file name.

[JeffBeck-NOAA]

Hey @gsketefian, what does the "- 1" do at the end of the line you changed?

[gsketefian]

@JeffBeck-NOAA It sets ie to the index of the character immediately before the "m" in "mosaic" in the file name. That's what the original line does, but I have to put in the -1 in order to make up for the fact that I removed the underscore from "_mosaic" in the original line (in order to allow the character before the "m" to be anything, e.g. a ".").