Add edge masks to default arguments of make_region_masks landice framework function

[andrewdnolan]

Description:
This PR adds edge region masks to the default options of the make_region_masks function within the mesh module of the landice framework.

The addition of edge masks for regions is needed the by the recent addition of SGH quantities to regional stats analysis member in MALI-Dev (MALI-Dev/E3SM#105).

Originally, we planned on adding vertex masks aswell, to forestall future problems. But after some experimentation with the antarctic/mesh_gen testcase, the additional masks slow down testcase execution considerably (~50%). As very few variables are defined on vertices, we've opted to leave them out of the defaults for now.

Checklist

• Document (in a comment titled Testing in this PR) any testing that was used to verify the changes

[andrewdnolan]

Testing

In order to test this PR, I've run the antarctic/mesh_gen testcase.

The testcase passes:

landice/antarctica/mesh_gen
  * step: mesh
  test execution:      SUCCESS

and the edge masks are present in the region mask files:

$ ncdump -h Antarctica_ismip6_regionMasks.nc

netcdf Antarctica_ismip6_regionMasks {
dimensions:
        nCells = 384370 ;
        nRegions = 16 ;
        StrLen = 18 ;
        string208 = 208 ;
        nEdges = 1158404 ;
variables:
        int regionEdgeMasks(nEdges, nRegions) ;
        int regionCellMasks(nCells, nRegions) ;
        char history(nRegions, string208) ;
                history:_Encoding = "utf-8" ;
        char regionNames(nRegions, StrLen) ;

The compass test case ran in 40:08 using the default config options, which is notable slowdown. Without the edge masks the testcase ran in 29:55 .

[matthewhoffman]

@andrewdnolan , thanks for taking care of this and testing out the impact on performance.