Improve Catch2 unit tests running

Now use separate steps to parse command line options and to run tests
This allows to output correctly help messages.
``
./unit_tests -h
``
now produces the expected output

tests/mpi_test_main.cpp

@@ -15,8 +15,14 @@ main(int argc, char* argv[])
   if (parallel::rank() != 0) {
     setenv("GCOV_PREFIX", "/dev/null", 1);
   }
+  Catch::Session session;
+  int result = session.applyCommandLine(argc, argv);
 
-  int result = Catch::Session().run(argc, argv);
+  if (result == 0) {
+    // Disable outputs from tested classes to the standard output
+    std::cout.setstate(std::ios::badbit);
+    result = session.run();
+  }
 
   Kokkos::finalize();
   parallel::Messenger::destroy();

tests/test_main.cpp

@@ -8,10 +8,14 @@ main(int argc, char* argv[])
 {
   Kokkos::initialize({4, -1, -1, true});
 
+  Catch::Session session;
+  int result = session.applyCommandLine(argc, argv);
+
+  if (result == 0) {
     // Disable outputs from tested classes to the standard output
     std::cout.setstate(std::ios::badbit);
-
-  int result = Catch::Session().run(argc, argv);
+    result = session.run();
+  }
 
   Kokkos::finalize();