Fixing bugs related to jfonfile cache plugin

* corrupt/invalid file causes tracebacks
* incorrect initialization of display/_display in BaseCacheModule class
* tweaking the way errors in get() on jsonfile caches work, to raise
  a proper AnsibleError in that situation so the playbook/task is stopped

Fixes #12708

lib/ansible/plugins/cache/__init__.py

@@ -20,6 +20,7 @@ __metaclass__ = type
 from collections import MutableMapping
 
 from ansible import constants as C
+from ansible.errors import AnsibleError
 from ansible.plugins import cache_loader
 
 try: