Commit 77de9653fd added a RetryRequest
exception to the policy engine for when items disappeared during policy
enforcement lookups. However, the API was not catching them for the
show and list operations.
This patch adds the decorators to the two methods to catch any
retry exception that may be emitted from the policy engine or
wherever else.
Closes-Bug: #1528031
Change-Id: If4aea5245cdbb2ea545e9a96d73386e3c21a3696
(cherry-picked from 2a27361cf5)