Optimize workflow execution steps

[tloisel1]

Is your feature request related to a problem? Please describe.
I have a workflow scenario that brings up 2 new autoscale groups, each with a wait directive that checks the health of the instances in the autoscale group. This process executes in serial so the wait directive from one will prevent the next autoscale group from being created.

Describe the solution you'd like
It would be nice if there was a variant of the wait directive that would execute asynchronously. The wait would still be honored at the Stage level of the workflow.

Describe alternatives you've considered
Another option would be to allow the wait directive to be declared as a directive under the Stage instead of the Action.