History needs to check if a file already exists when it decides it is time to write a new file

[bena-nasa]

The title says it all, I'll be making a PR here soon.

Each time History runs, it must make a determine if it is time to write a collection and if the file is a new file or if we are appending to the file like in the case when you have multiple time steps per file. We do not check that if the file is new, that it does not already exist. I'm going to put that protection in because I wasted many hours chasing a problem with the DAS because we do not have this check which leads to a more confusing error later that would have been clear had we caught this in the gridcomp. Note the issue I found in the DAS is not a MAPL issue other than that we let an error get too far; the DAS scripts need to remove files as I detailed in this issue I opened in the DAS repo:

GEOS-ESM/GEOSadas#188