Use safer HTTP 409 message check in enable_rhrepo (SatelliteQE#21916)

Author: vsedmik

robottelo/host_helpers/api_factory.py

@@ -133,7 +133,7 @@ def enable_rhrepo_and_fetchid(
             if (
                 not strict
                 and e.response.status_code == 409
-                and 'repository is already enabled' in e.response.json()['displayMessage']
+                and 'repository is already enabled' in e.response.json().get('message', '')
             ):
                 pass
             else: