Update sample-jobdef.clj to have the actual behavior of wait-on-step reflected in the comments.

Fixed comment on the behaviour of wait-on-step.  The comments on the function in src/main/clj/lemur/core.clj are correct, but the statement about throwing exceptions that was here was not correct.
Merge pull request #21 from kasterma/patch-1

Update sample-jobdef.clj to have the actual behavior of wait-on-step ref...