style: clean up exception definitions in package.py
style: clean up exception definitions in package.py

krafczyk/spack,mfherbst/spack,iulian787/spack,krafczyk/spack,krafczyk/spack,LLNL/spack,LLNL/spack,mfherbst/spack,LLNL/spack,LLNL/spack,mfherbst/spack,iulian787/spack,iulian787/spack,LLNL/spack,iulian787/spack,krafczyk/spack,iulian787/spack,mfherbst/spack,mfherbst/spack,krafczyk/spack