petsc: update to latest 3.8 version [and include 3.7.7] (#5723)
petsc: update to latest 3.8 version [and include 3.7.7] (#5723)

Also fix flake8 warning "import os should be before import sys"
iulian787/spack,skosukhin/spack,iulian787/spack,iulian787/spack,matthiasdiener/spack,lgarren/spack,matthiasdiener/spack,tmerrick1/spack,mfherbst/spack,skosukhin/spack,krafczyk/spack,lgarren/spack,lgarren/spack,tmerrick1/spack,matthiasdiener/spack,krafczyk/spack,krafczyk/spack,iulian787/spack,EmreAtes/spack,lgarren/spack,LLNL/spack,matthiasdiener/spack,mfherbst/spack,EmreAtes/spack,skosukhin/spack,skosukhin/spack,tmerrick1/spack,tmerrick1/spack,LLNL/spack,krafczyk/spack,mfherbst/spack,tmerrick1/spack,mfherbst/spack,EmreAtes/spack,EmreAtes/spack,LLNL/spack,LLNL/spack,iulian787/spack,krafczyk/spack,lgarren/spack,mfherbst/spack,LLNL/spack,skosukhin/spack,EmreAtes/spack,matthiasdiener/spack