Issue 759: remove grok from swarming libraries.

This corrects issue 759.  References to grok renamed to nupic.  References
to Grok either removed or renamed to Nupic.  Passes unit tests locally, also
ran locally on sine-prediction and hot-gym swarms.
Removes StreamDisappearedError

I went ahead and removed this, as it's not being raised anywhere, and I removed the check for it in my previous commit
remove import of StreamDisappearedError

Forgot to remove StreamDisappearedError during last commit.
Merge pull request #925 from moorejpdx/grok_cleanup_for_swarming_libraries

Grok cleanup for swarming libraries