Add DeleteAttribute support to the client

This change adds DeleteAttribute support to the ProxyKmipClient,
leveraging the new generic request capability in the underlying
KMIPProxy client. Going forward all new attribute support will
leverage the new request capability and older supported operations
will be migrated to use it as well, with the ultimate vision
being a final merger of the two client classes into one easy to
use architecture. New unit tests have been added to cover the new
client additions.

Partially implements #547

kmip/tests/unit/pie/test_client.py

@@ -24,6 +24,7 @@ from kmip.core import objects as obj
 
 from kmip.core.factories import attributes
 from kmip.core.messages import contents
+from kmip.core.messages import payloads
 from kmip.core.primitives import DateTime
 
 from kmip.services.kmip_client import KMIPProxy
@@ -758,6 +759,41 @@ class TestProxyKmipClient(testtools.TestCase):
             KmipOperationFailure, error_msg,
             client.create_key_pair, *args)
 
+    @mock.patch(
+        "kmip.pie.client.KMIPProxy",
+        mock.MagicMock(spec_set=KMIPProxy)
+    )
+    def test_delete_attribute(self):
+        """
+        Test that the client can delete an attribute.
+        """
+        request_payload = payloads.DeleteAttributeRequestPayload(
+            unique_identifier="1",
+            attribute_name="Object Group",
+            attribute_index=2
+        )
+        response_payload = payloads.DeleteAttributeResponsePayload(
+            unique_identifier="1",
+            attribute=None
+        )
+
+        with ProxyKmipClient() as client:
+            client.proxy.send_request_payload.return_value = response_payload
+
+            unique_identifier, attribute = client.delete_attribute(
+                "1",
+                attribute_name="Object Group",
+                attribute_index=2
+            )
+
+            args = (
+                enums.Operation.DELETE_ATTRIBUTE,
+                request_payload
+            )
+            client.proxy.send_request_payload.assert_called_with(*args)
+            self.assertEqual("1", unique_identifier)
+            self.assertIsNone(attribute)
+
     @mock.patch(
         'kmip.pie.client.KMIPProxy', mock.MagicMock(spec_set=KMIPProxy)
     )