Get Cray OS version from PrgEnv-cray (#10774)
Get Cray OS version from PrgEnv-cray (#10774)

The regex used for finding the Cray OS version from the PrgEnv-cray
module was not exact and was at times pulling the version from other
PrgEnv modules. This updates the regular expression to be more exact.
LLNL/spack,LLNL/spack,LLNL/spack,iulian787/spack,iulian787/spack,iulian787/spack,LLNL/spack,iulian787/spack,iulian787/spack,LLNL/spack