Set some CMake variables in Conda python packages

CMAKE_FIND_ROOT to be able to find external libraries like openmesh
CMAKE_INSTALL_PREFIX for a possible later "make install"

utilities/conda/withLbm/build.sh

 mkdir build
 cd build
-export BOOST_ROOT=$PREFIX
 
-cmake .. -DWALBERLA_BUILD_WITH_PYTHON=ON -DWALBERLA_BUILD_WITH_PYTHON_MODULE=ON -DWALBERLA_BUILD_WITH_PYTHON_LBM=ON
+cmake \
+   -DCMAKE_FIND_ROOT_PATH=${PREFIX} \
+   -DCMAKE_INSTALL_PREFIX=${PREFIX} \
+   -DWALBERLA_BUILD_WITH_PYTHON=ON \
+   -DWALBERLA_BUILD_WITH_PYTHON_MODULE=ON \
+   -DWALBERLA_BUILD_WITH_PYTHON_LBM=ON \
+   ..
 
 make -j ${CPU_COUNT} pythonModuleInstall

utilities/conda/withoutLbm/build.sh

 mkdir build
 cd build
-export BOOST_ROOT=$PREFIX
 
-cmake .. -DWALBERLA_BUILD_WITH_PYTHON=ON -DWALBERLA_BUILD_WITH_PYTHON_MODULE=ON -DWALBERLA_BUILD_WITH_OPENMESH=ON
+cmake \
+   -DCMAKE_FIND_ROOT_PATH=${PREFIX} \
+   -DCMAKE_INSTALL_PREFIX=${PREFIX} \
+   -DWALBERLA_BUILD_WITH_PYTHON=ON \
+   -DWALBERLA_BUILD_WITH_PYTHON_MODULE=ON \
+   -DWALBERLA_BUILD_WITH_PYTHON_LBM=ON \
+   ..
 
 make -j ${CPU_COUNT} pythonModuleInstall