IMPALA-1103: Fix cancellation check in FetchInternal() to use the query status.

We recently changed user-initiated cancellation to not set the query state
to EXCEPTION. In FetchInternal() we relied on the previous behavior for
detecting cancellations/errors after BlockOnWait().
This patch fixes the cancellation/error check to use the query status
instead of the query state.

Change-Id: I48b4834e77b6e692fb6722637fb9fd5d8c8d9d97
Reviewed-on: http://gerrit.ent.cloudera.com:8080/3597
Reviewed-by: Alex Behm <alex.behm@cloudera.com>
Tested-by: jenkins
Reviewed-on: http://gerrit.ent.cloudera.com:8080/3600