Fix test pillar: use key_url for cassandra repo

Change-Id: Ib18101299366a6110be9ab937a670de3c746a6e1
Related-PROD: PROD-27054
diff --git a/tests/pillar/cassandra.sls b/tests/pillar/cassandra.sls
index 64ed6c4..d0e9848 100644
--- a/tests/pillar/cassandra.sls
+++ b/tests/pillar/cassandra.sls
@@ -5,5 +5,4 @@
       cassandra-21x:
         source: "deb [arch=amd64] http://www.apache.org/dist/cassandra/debian 21x main"
         architectures: amd64
-        key_server: pool.sks-keyservers.net
-        key_id: A278B781FE4B2BDA
+        key_url: "https://www.apache.org/dist/cassandra/KEYS"