Modified Case expression tests in exprs.test

Change-Id: I65cee2e14291db8bf14a428715b08dac475b863a
Reviewed-on: http://gerrit.ent.cloudera.com:8080/3485
Reviewed-by: Paden Tomasello <paden.tomasello@cloudera.com>
Tested-by: jenkins
Reviewed-on: http://gerrit.ent.cloudera.com:8080/3601