Bugfix 1886 main_v10.0 grid_diag

[JohnHalleyGotway]

Pull Request Testing

@georgemccabe I'm including you on this PR for your code review but also to alert you that the Grid-Diag output variables will change from type int to int64. Note that ncdiff does NOT flag this as a difference.

Also note that I'll be submitting a similar PR to fix this in develop but will include a couple more changes.

• Describe testing already performed for these changes:
  
  Manually tested a run of grid_diag using MET version 10.0.0 that replicates the integer overflow problem. Switched from vectors of type to vectors of type , retested, and confirmed that the overflow problem is gone. Also histograms in the NetCDF output files are now of type ncInt64 instead of int.

Ran unit_grid_diag.xml to confirm that all existing tests run fine.

• Recommend testing for the reviewer(s) to perform, including the location of input datasets, and any additional instructions:
  
  Review the code changes.

• Do these changes include sufficient documentation updates, ensuring that no errors or warnings exist in the build of the documentation? [No]
  The existing grid_diag documentation makes no mention of the NetCDF output variable type. So there's no documentation to update.

• Do these changes include sufficient testing updates? [No]
  I chose not to add a new unit test to exercise integer overflow. Adding a time/compute intensive unit test doesn't seem worth it.

• Will this PR result in changes to the test suite? [Yes]
  
  If yes, describe the new output and/or changes to the existing output:
  
  The variable types for all existing grid_diag NetCDF output files will change from "int" to "int64".

• Please complete this pull request review by [8/23/2021].
  

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[georgemccabe]

The change appear to be isolated to changing the C data type from int to long long and the NetCDF data type from ncInt to ncInt64 for a single field. This will likely cause differences in the METplus use case tests because these values will slightly change in the stat output. After this PR and the develop equivalent are merged, the METplus tests should be rerun to ensure that the new differences are isolated to these expected changes. I approve of these changes.

[JohnHalleyGotway]

Since @jwolff-ncar is able to run using MET version 10.0.0 after setting up her configuration the way she intended, I will proceed with PR #1888 to fix this in the develop branch and fix it in version 10.1.0. But I will NOT merge in the changes for PR #1887 to fix this for MET version 10.0.1. Changing the Grid-Diag NetCDF output variable from int to int64 seems like too big of a change for a bugfix release, especially since we don't have a user who actually needs it right now.