oc_atomic_container: Workaround for invalid json from atomic command

When no other containers are present and one attempts to list containers
via the atomic command with the --json flag an empty string is returned.
If a json.loads is used on this value an error is raised. This change
adds a workaround to fall back to '[]' when an empty string is returned
from the atomic containers command.

roles/lib_openshift/library/oc_atomic_container.py

@@ -159,7 +159,9 @@ def core(module):
         module.fail_json(rc=rc, msg=err)
         return
 
-    containers = json.loads(out)
+    # NOTE: "or '[]' is a workaround until atomic containers list --json
+    # provides an empty list when no containers are present.
+    containers = json.loads(out or '[]')
     present = len(containers) > 0
     old_image = containers[0]["image_name"] if present else None
 

roles/lib_openshift/src/ansible/oc_atomic_container.py

@@ -95,7 +95,9 @@ def core(module):
         module.fail_json(rc=rc, msg=err)
         return
 
-    containers = json.loads(out)
+    # NOTE: "or '[]' is a workaround until atomic containers list --json
+    # provides an empty list when no containers are present.
+    containers = json.loads(out or '[]')
     present = len(containers) > 0
     old_image = containers[0]["image_name"] if present else None