IMPALA-1009: UDF/UDA leaks should not fail queries

With this change, leaky UDFs built with the SDK will still fail when
using the test harness, but leaky UDFs running in Impala will only
trigger a warning. This change also updates the test infrastructure to
always check for non-fatal errors/warnings.

Change-Id: I5615349b9d691e4eddea3e03e152ef12e73835e7
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2844
Reviewed-by: Skye Wanderman-Milne <skye@cloudera.com>
Tested-by: jenkins