Force gstats tasks to run sequentially

[DJDavies2]

Description

Force the gstats task to run sequentially to ensure they don't all try to write to the same output file.

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

[DJDavies2]

It would be better if the tasks all wrote to different files, but that would require code changes.

[wdeconinck]

Thanks for the proposal.
Rather than having tests depend on each other we can also use cmake's RESOURCE_LOCK test property, such as was also done for some dr_hook tests.

foreach( test fiat_test_gstats_csv_output_mpi0
              fiat_test_gstats_csv_output_mpi1
              fiat_test_gstats_csv_output_mpi2 )
  if( TEST ${test} )
    set_tests_properties(${test} PROPERTIES RESOURCE_LOCK gstats_csv_output )
  endif()
endforeach()

[DJDavies2]

Thanks for the proposal. Rather than having tests depend on each other we can also use cmake's RESOURCE_LOCK test property, such as was also done for some dr_hook tests.

foreach( test fiat_test_gstats_csv_output_mpi0
              fiat_test_gstats_csv_output_mpi1
              fiat_test_gstats_csv_output_mpi2 )
  if( TEST ${test} )
    set_tests_properties(${test} PROPERTIES RESOURCE_LOCK gstats_csv_output )
  endif()
endforeach()

I've implemented this.

[wdeconinck]

Thanks @DJDavies2 for fixing and addressing review.