Adjust options to prometheus 1.6

Change-Id: I366b9fbef37bde5110515e0f8ac13110d5ab4b8b
diff --git a/tests/pillar/server.sls b/tests/pillar/server.sls
index 64f31f2..e29422f 100644
--- a/tests/pillar/server.sls
+++ b/tests/pillar/server.sls
@@ -56,8 +56,7 @@
       local:
         engine: "persisted"
         retention: "360h"
-        memory_chunks: 1048576
-        max_chunks_to_persist: 524288
+        target_heap_size: 3221225472
         num_fingerprint_mutexes: 4096
     alertmanager:
       notification_queue_capacity: 10000