[FLINK-7300] Fix unstable Kafka end-to-end tests

Instead of specifying a timeout for the console consumer we now speciy
an uppper message boundary that matches our expected number of messages.
The timout was to unstable because it could sometimes return even though
messages were in fact available.

test-infra/end-to-end-test/test_streaming_kafka010.sh

@@ -73,24 +73,7 @@ $FLINK_DIR/bin/flink run -d build-target/examples/streaming/Kafka010Example.jar
 # send some data to Kafka
 echo -e "hello\nwhats\nup" | $KAFKA_DIR/bin/kafka-console-producer.sh --broker-list localhost:9092 --topic test-input
 
-# wait at most (roughly) 5 minutes until the results are there
-for i in {1..300}; do
- DATA_FROM_KAFKA=$($KAFKA_DIR/bin/kafka-console-consumer.sh --bootstrap-server localhost:9092 --topic test-output --from-beginning --timeout-ms 0 2> /dev/null)
-
- # make sure we have actual newlines in the string, not "\n"
- EXPECTED=$(printf "PREFIX:hello\nPREFIX:whats\nPREFIX:up")
-
- if [[ "$DATA_FROM_KAFKA" == "$EXPECTED" ]]; then
- echo -e "Retrieved data from Kafka: --$DATA_FROM_KAFKA--"
- break
- fi
-
- echo "Waiting for results from Kafka..."
- sleep 1
-done
-
-# verify again to set the PASS variable
-DATA_FROM_KAFKA=$($KAFKA_DIR/bin/kafka-console-consumer.sh --bootstrap-server localhost:9092 --topic test-output --from-beginning --timeout-ms 0 2> /dev/null)
+DATA_FROM_KAFKA=$($KAFKA_DIR/bin/kafka-console-consumer.sh --bootstrap-server localhost:9092 --topic test-output --from-beginning --max-messages 3 2> /dev/null)
 
 # make sure we have actual newlines in the string, not "\n"
 EXPECTED=$(printf "PREFIX:hello\nPREFIX:whats\nPREFIX:up")