Disable test_fetch_first and test_session_expiration.

This patch disables these two tests to unblocks builds. Tested the custom_cluster tests
locally to confirm that they do indeed get skipped.

Change-Id: Ie6e67daf7e5705c2227e19a079682e87ad35ee6c
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/4381
Reviewed-by: Ishaan Joshi <ishaan@cloudera.com>
Tested-by: jenkins