[test] Use ignore option for test script instead of zero threshold

test/discretization/CMakeLists.txt

test/freeflow/navierstokes/donea/CMakeLists.txt

test/freeflow/shallowwater/bowl/CMakeLists.txt

test/freeflow/shallowwater/poiseuilleflow/CMakeLists.txt

test/io/gridmanager/CMakeLists.txt

test/porousmediumflow/1p/periodicbc/CMakeLists.txt

test/porousmediumflow/co2/CMakeLists.txt

test/porousmediumflow/richards/lens/CMakeLists.txt