Fix retrying call, "retry_on_exception" argument excepts a callable.
Fix retrying call, "retry_on_exception" argument excepts a callable.

StackStorm/st2,Plexxi/st2,StackStorm/st2,Plexxi/st2,nzlosh/st2,Plexxi/st2,Plexxi/st2,nzlosh/st2,StackStorm/st2,nzlosh/st2,nzlosh/st2,StackStorm/st2