Increase collection rate for Cassandra metrics

The metrics are now collected at the same interval (50s) than the other
potentially slow answering services

Change-Id: I1228a9729b927e903932c187efdb8708e5128fd5
diff --git a/opencontrail/files/collectd_cassandra_jmx.conf b/opencontrail/files/collectd_cassandra_jmx.conf
index a074afd..26a8794 100644
--- a/opencontrail/files/collectd_cassandra_jmx.conf
+++ b/opencontrail/files/collectd_cassandra_jmx.conf
@@ -2,6 +2,7 @@
 {%- from "linux/map.jinja" import system with context %}
 <LoadPlugin java>
   Globals false
+  Interval 50
 </LoadPlugin>
 
 <Plugin "java">