Fix invalid exception class usage.
Fix invalid exception class usage.

We simply swallow error messages from OperationFailureError class, we
should throw ResourceNotFoundError instead so the error message is
correctly printed to the console.

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