Stop setting query state to EXCEPTION for non-exception cases.

We were setting the state to exception on Cancel() all the time.
We use the cancellation path as the normal cleanup path so this
gets called even when the query went fine (e.g. UnregisterQuery
calls Cancel()). We had already plumbed through a 'cause' argument
to differentiate.

Change-Id: Icf1091c165dec36d3dad7ce308367bbbc9edee4f
Reviewed-on: http://gerrit.ent.cloudera.com:8080/3524
Reviewed-by: Nong Li <nong@cloudera.com>
Tested-by: jenkins
Reviewed-on: http://gerrit.ent.cloudera.com:8080/3575