IMPALA-7840: add missing error to test_concurrent_schema_change
IMPALA-7840: add missing error to test_concurrent_schema_change

test_concurrent_schema_change runs a series of alters and inserts on
the same Kudu table concurrently to ensure that Impala can handle this
without crashing.

There is a list of expected error messages in the test. One possible
legitimate error is missing, causing the test to sometimes be flaky.

This patch adds that error message to the test.

Change-Id: Ibc01e1244e05be30343c05b5a0f8676f4d4603d2
Reviewed-on: http://gerrit.cloudera.org:8080/11913
Reviewed-by: Thomas Marshall <19143d3de8b13ab65aabdc921d14db5a16735b95@cmu.edu>
Tested-by: Impala Public Jenkins <039b6b20426ff68ebe492b3021890d8c8fd010c9@cloudera.com>

cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala