IMPALA-2993: don't check for "Failed to allocate buffer for collection" error

This test query is supposed to check the error path for when a
collection buffer cannot be allocated. However, it's flaky because the
collection allocations are not very big (< 2KB), so it's possible for
a different operator to trigger OOM.

I think the correct solution is to create a test file that contains
very large collections, so a large collection allocation will trigger
OOM, rather than many small collection allocations. For now though,
let's disable the specific collection allocation check to unblock the
build, even though we risk losing coverage.

Change-Id: Iab4c9b605186926c522cf692246a37882fbdfcdb
Reviewed-on: http://gerrit.cloudera.org:8080/2208
Reviewed-by: Skye Wanderman-Milne <skye@cloudera.com>
Tested-by: Internal Jenkins

testdata/workloads/functional-query/queries/QueryTest/nested-types-tpch.test

@@ -162,6 +162,8 @@ BIGINT,BIGINT
 ---- QUERY
 # IMPALA-2376
 # Set memory limit low enough to get the below query to consistently fail.
+# TODO: change query and/or table so we can consistently check for the following error:
+# Failed to allocate buffer for collection '...'.
 set mem_limit=4m;
 select max(cnt) from customer c,
 (select count(l_returnflag) cnt from c.c_orders.o_lineitems) v;
@@ -169,7 +171,6 @@ select max(cnt) from customer c,
 BIGINT
 ---- CATCH
 Memory limit exceeded
-Failed to allocate buffer for collection 'tpch_nested_parquet.customer.c_orders.item.o_lineitems'.
 ====
 ---- QUERY
 # IMPALA-2473: Scan query with large row size leading to oversized batches.