Handle non-existant plan when getting deployment status

Instead of showing a traceback when requesting the deployment status of
a non-existant plan, show a useful message instead.

Change-Id: I3b10361fd17e1068e46a219b8081451f5c7ed035
Depends-On: Ic0333c0726b16d284a7cc54bc68e16ea1c9ebc4d
Closes-Bug: #1792637

releasenotes/notes/handle-no-deployment-status-a8f73f887f0f158f.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - When requesting the deployment status of a non-existant plan, instead of
+    showing a traceback, show a helpful message indicating there is no status.

tripleoclient/v1/overcloud_deploy.py

@@ -953,6 +953,9 @@ class GetDeploymentStatus(command.Command):
             plan=plan
         )
 
+        if not status:
+            return
+
         payload = status['workflow_status']['payload']
         execution = payload['execution']
         table = PrettyTable(