Heat used a 1MB payload size for returned output. YUM's output exceeded this limit if updating a high number of packages on the Overcloud, which caused 'openstack overcloud update' to fail. This fix adds the '-q' option to YUM during an Overcloud update. This option sets the output to quiet mode, which reduced the output. YUM's output no longer exceeds Heat's limit and 'openstack overcloud update' succeeds.