Fix app cred client unit test name

A copy-paste error led to one of the application credential client unit
tests being named 'test_delete_trust' which is not correct in this
context. This change corrects the test name

Change-Id: I494b5ef08ba6c906827705a2a16d72e95e37af12
diff --git a/tempest/tests/lib/services/identity/v3/test_application_credentials_client.py b/tempest/tests/lib/services/identity/v3/test_application_credentials_client.py
index 9bf9b68..2774c44 100644
--- a/tempest/tests/lib/services/identity/v3/test_application_credentials_client.py
+++ b/tempest/tests/lib/services/identity/v3/test_application_credentials_client.py
@@ -146,7 +146,7 @@
     def test_list_application_credential_with_bytes_body(self):
         self._test_list_app_creds(bytes_body=True)
 
-    def test_delete_trust(self):
+    def test_delete_application_credential(self):
         self.check_service_client_function(
             self.client.delete_application_credential,
             'tempest.lib.common.rest_client.RestClient.delete',