added cassandra validation and maintenance playbooks

cassandra-maintenance.yml

diff --git a/cassandra-maintenance.yml b/cassandra-maintenance.yml
index 0e0de87..2941879 100644
--- a/cassandra-maintenance.yml
+++ b/cassandra-maintenance.yml
@@ -1,5 +1,7 @@
 ---
 - hosts: ds
+  gather_facts: no
+  serial: 1
   roles:
   - apigee-opdk-cassandra-repair
   - apigee-opdk-cassandra-rebuild