Updated release_notes and release version to 1.1.7 including Kerberos related changes
Fix tests for testStartVoldemortCluster to not consume so much memory

test/common/voldemort/ServerTestUtils.java
- remove stress test from normal testing
- test the method startVoldemortCluster once and confirm it returns a non-null Cluster object

test/common/voldemort/ServerTestUtils.java
- clarified a comment