Check for required hosts before running gatling tests
Check for required hosts before running gatling tests

The gatling tests require all both mongo and spark to be specified
in order to run, so check to make sure they're set and give an
error message if they aren't.

NextCenturyCorporation/neon,NextCenturyCorporation/neon,codeaudit/neon-1,codeaudit/neon-1