message: lowering the nprocs in dockerfile ci
diff: from xacc/ubuntu:18.04
  run git clone --recursive -b xacc-devel https://github.com/eclipse/xacc && cd xacc && mkdir build && cd build \
  && cmake .. -DXACC_BUILD_TESTS=TRUE \
  - && make -j$(nproc) install && PYTHONPATH=$HOME/.xacc ctest --output-on-failure
  + && make -j24 install && PYTHONPATH=$HOME/.xacc ctest --output-on-failure
  