Set MPIEXEC_EXECUTABLE in gcovr and lcov tests

Will now actually test MPI files

.gitlab-ci.yml

@@ -337,7 +337,7 @@ build-gnu-gcov:
     - export PYTHONPATH=$HOME/intel/oneapi/intelpython/latest/lib/python3.7/site-packages/:`pwd`/cpp_sisso_gnu_gcov_env/lib/python3.7/site-packages/
     - mkdir build_gcov/
     - cd build_gcov/
-    - cmake -DCMAKE_CXX_COMPILER=g++ -DCMAKE_C_COMPILE=gcc -DCMAKE_BUILD_TYPE="Coverage" -DBUILD_TESTS=ON -DBUILD_PARAMS=ON -DBUILD_PYTHON=ON  -DCMAKE_INSTALL_PREFIX=../gnu_gcov/ ../
+    - cmake -DCMAKE_CXX_COMPILER=g++ -DCMAKE_C_COMPILE=gcc -DCMAKE_BUILD_TYPE="Coverage" -DMPIEXEC_EXECUTABLE=/usr/bin/mpiexec -DBUILD_TESTS=ON -DBUILD_PARAMS=ON -DBUILD_PYTHON=ON  -DCMAKE_INSTALL_PREFIX=../gnu_gcov/ ../
     - make install
     - make coverage
     - cd ../
@@ -357,7 +357,7 @@ build-gnu-lcov:
     - export PYTHONPATH=$HOME/intel/oneapi/intelpython/latest/lib/python3.7/site-packages/:`pwd`/cpp_sisso_gnu_lcov_env/lib/python3.7/site-packages/
     - mkdir build_lcov/
     - cd build_lcov/
-    - cmake -DCMAKE_CXX_COMPILER=g++ -DCMAKE_C_COMPILE=gcc -DCMAKE_BUILD_TYPE="Coverage" -DBUILD_TESTS=ON -DBUILD_PARAMS=ON -DBUILD_PYTHON=ON -DCMAKE_INSTALL_PREFIX=../gnu_lcov/ ../
+    - cmake -DCMAKE_CXX_COMPILER=g++ -DCMAKE_C_COMPILE=gcc -DCMAKE_BUILD_TYPE="Coverage" -DMPIEXEC_EXECUTABLE=/usr/bin/mpiexec -DBUILD_TESTS=ON -DBUILD_PARAMS=ON -DBUILD_PYTHON=ON -DCMAKE_INSTALL_PREFIX=../gnu_lcov/ ../
     - make install
     - make coverage_html
     - cd ../