added cassandra validation and maintenance playbooks

cassandra-maintenance.yml

diff --git a/cassandra-maintenance.yml b/cassandra-maintenance.yml
index 63ed278..a4cca0a 100644
--- a/cassandra-maintenance.yml
+++ b/cassandra-maintenance.yml
@@ -3,5 +3,5 @@
   gather_facts: no
   serial: 1
   roles:
-  - { role: apigee-opdk-cassandra-repair }
   - { role: apigee-opdk-cassandra-rebuild, opdk_region: 'dc-1' }
+  - { role: apigee-opdk-cassandra-repair }