Description of the problem: 
After deleting the pod of a workflow that has running instances, trying to abort the instance after the workflow pod has been deleted and come up again results in a 500 error.

How reproducible: 100%

Steps to reproduce:

1. Deploy with Orchestrator chart 0.2.4

2. Deploy a workflow, and while it is running, go to the cluster and delete the workflow pod (or scale the deployment to 0)

3. Wait for the pod to come up, and try to abort the running workflow.

Actual results: 
Aborting the workflow fails with 500 error. The workflow remains in Active state forever.

Expected results:
Aborting the workflow should succeed.