MPAS I/O hang during Parallel NetCDF header reallocation

[amstokely]

If MPAS encounters an I/O scenario that requires Parallel NetCDF to reallocate the file header (e.g., when ncmpi_enddef is called and the header has grown beyond its preallocated padding while in define mode), an I/O hang can occur. This was the root cause of issue 384 in MPAS-Workflow. In this case, the hang occurred when overwriting the config_block_decomp_file_prefix global attribute in the analysis NetCDF file with a longer string. Using Forge DDT, the hang was traced to the call to ncmpi_enddef following this attribute update.