Ensure show on absent appcreds raises exception

Currently, running ``application credential show`` on a
non-existent appcred will exit normally and display a
formatted application credential with no data, despite
the Keystone API returning a 404.

Ensure that querying a non-existent application
credential raises an exception message and an exit-code
1 to the user.

Closes-Bug: #2126565
Change-Id: I597d2d4064f1020c5ac40862ecc556f3c94b53eb
Signed-off-by: Matt Anson <matta@stackhpc.com>

Author: m-bull

openstackclient/identity/v3/application_credential.py

@@ -352,7 +352,7 @@ def take_action(self, parsed_args):
         user_id = conn.config.get_auth().get_user_id(conn.identity)
 
         application_credential = identity_client.find_application_credential(
-            user_id, parsed_args.application_credential
+            user_id, parsed_args.application_credential, ignore_missing=False
         )
 
         return _format_application_credential(application_credential)

openstackclient/tests/unit/identity/v3/test_application_credential.py

@@ -457,7 +457,7 @@ def test_application_credential_show(self):
         columns, data = self.cmd.take_action(parsed_args)
 
         self.identity_sdk_client.find_application_credential.assert_called_with(
-            user_id, self.application_credential.id
+            user_id, self.application_credential.id, ignore_missing=False
         )
 
         self.assertEqual(self.columns, columns)

releasenotes/notes/bug-2126565-a119ac242d9ac795.yaml

@@ -0,0 +1,8 @@
+---
+fixes:
+  - |
+    Running ``openstack application credential show`` on
+    a non-existent application credential does not
+    raise an exception.
+
+    [Bug `2126565 <https://bugs.launchpad.net/python-openstackclient/+bug/2126565>`_]