CMake: improve testsuite driver performance

[tamiko]

Some preliminary results:

% ctest -R "petsc_step-27.mpirun=2.debug" # first run:
1/2 Test #9807: test_dependency/mpi.petsc_step-27.debug.executable ...   Passed   14.15 sec
2/2 Test #9811: mpi/petsc_step-27.mpirun=2.debug .....................   Passed    3.08 sec
% ctest -R "petsc_step-27.mpirun=2.debug" # rerun:
1/2 Test #9807: test_dependency/mpi.petsc_step-27.debug.executable ...   Passed    0.15 sec
2/2 Test #9811: mpi/petsc_step-27.mpirun=2.debug .....................   Passed    0.14 sec

As compared to a baseline test with make:

% ctest -R "petsc_step-27.mpirun=2.debug" # first run
1/2 Test #9807: test_dependency/mpi.petsc_step-27.debug.executable ...   Passed   16.38 sec
2/2 Test #9811: mpi/petsc_step-27.mpirun=2.debug .....................   Passed    5.42 sec
% ctest -R "petsc_step-27.mpirun=2.debug" # rerun
1/2 Test #9807: test_dependency/mpi.petsc_step-27.debug.executable ...   Passed    2.36 sec
2/2 Test #9811: mpi/petsc_step-27.mpirun=2.debug .....................   Passed    2.33 sec

[bangerth]

I don't think I understand what you're doing here, but got a couple of suggestions.

[tamiko]

@bangerth
This is a very preliminary version of some more massive rewriting effort.

My goal is to significantly reduce the overhead introduced by make in the testsuite. For example, for some tests make might contribute to north of 25% of the total runtime of the test.

[tamiko]

New PR incoming.