Pipeline DISCARD support (redis#1565)

closes redis#1539

Part of redis#1546

(cherry picked from commit febede1)

cr: https://code.amazon.com/reviews/CR-57987360

Author: chayim

tests/test_pipeline.py

@@ -1,11 +1,9 @@
 import pytest
 
 import redis
-from .conftest import wait_for_command, skip_if_server_version_lt, \
-    skip_if_cluster_mode
+from .conftest import wait_for_command, skip_if_server_version_lt
 
 
-@skip_if_cluster_mode()
 class TestPipeline:
     def test_pipeline_is_true(self, r):
         "Ensure pipeline instances are not false-y"