Suppress fileIO.chpl primer for KNC.

IO is not (yet) understood with KNC.
Suppress pidigits.chpl when testing LLVM.

GMP and LLVM do not (yet) work together.
Call ./nightly with llvm suppressions for llvm testing.
Setup common-knc.bash to use suppressions.

Vanilla intel (non PrgEnv) tests do not run yet. But this will help if they
ever do.
fix typo
Update comment for clarity based on feedback from @sungeun
Merge pull request #531 from thomasvandoren/suppress-llvm-and-knc-issues

Suppress llvm and knc issues.

@bradcray made a good suggestion that llvm and knc testing should use suppressions to track the
couple tests that are having issues. This updates the nightly testing scripts to suppress pidigits failures
for llvm and fileIO failures for knc.

reviewed by @sungeun