Problem with QE GPU install script

[wyang0]

There are some issues with the current quantum_espresso/install_qe_gpu.sh script.
- cd qe-7.1-qmcpack-gpu needs to be cd qe-7.2-qmcpack
- -DQE_ENABLE_OPENACC=ON should be -DQE_ENABLE_OPENACC=ON \
- NERSC QE webpage suggests to load the PrgEnv-nvidia module but the script doesn't load it

A user reports that there is still a build problem with version 7.2 even with the corrections, and a modified script works with version 7.3 (see INC0216095). I have verified on those two points.

Please review the suggested changes and update the script.