[FAB-5252] Fix make failures for non-default versions

`make kafka` will fail even if the user edits the `KAFKA_VERSION`,
`KAFKA_DOWNLOAD_SHA1`, and `SCALA_VERSION` values. This changeset
addresses this.

Change-Id: I8937280dae1085e98d3ae6b949c0bfb70b4f2ec6
Signed-off-by: Kostas Christidis <kostas@christidis.io>

Author: kchristidis

docs/source/kafka.rst

@@ -168,7 +168,9 @@ also set the preferred size of blocks by setting the
 ``Orderer.Batchsize.PreferredMaxBytes`` key. Kafka offers higher throughput when
 dealing with relatively small messages; aim for a value no bigger than 1 MiB.
 
-2. **Using environment variables to override settings.** You can override a
+2. **Using environment variables to override settings.** When using the sample
+Kafka and Zookeeper Docker images provided with Hyperledger Fabric (see
+``images/kafka`` and ``images/zookeeper`` respectively), you can override a
 Kafka broker or a ZooKeeper server's settings by using environment variables.
 Replace the dots of the configuration key with underscores --
 e.g. ``KAFKA_UNCLEAN_LEADER_ELECTION_ENABLE=false`` will allow you to override
@@ -184,9 +186,11 @@ Supported Kafka versions for v1 are ``0.9`` and ``0.10``. (Hyperledger Fabric
 uses the `sarama client library <https://github.com/Shopify/sarama>`_
 and vendors a version of it that supports Kafka 0.9 and 0.10.)
 
-Out of the box the Kafka version defaults to ``0.9.0.1``. If you wish to use a
-different supported version, specify a supported version using the
-``Kafka.Version`` key in ``orderer.yaml``.
+Out of the box the Kafka version defaults to ``0.9.0.1``. The sample Kafka
+image provided by Hyperledger Fabric matches this default version. If you are
+not using the sample Kafka image provided by Hyperledger Fabric, ensure that
+you specify your Kafka cluster's Kafka version using the ``Kafka.Version`` key
+in ``orderer.yaml``.
 
 The current supported Kafka versions are:
 

images/kafka/Dockerfile.in

@@ -8,7 +8,7 @@ ENV SCALA_VERSION=2.11 \
     KAFKA_VERSION=0.9.0.1 \
     KAFKA_DOWNLOAD_SHA1=FC9ED9B663DD608486A1E56197D318C41813D326
 
-RUN curl -fSL "http://www-us.apache.org/dist/kafka/0.9.0.1/kafka_${SCALA_VERSION}-${KAFKA_VERSION}.tgz" -o kafka_${SCALA_VERSION}-${KAFKA_VERSION}.tgz \
+RUN curl -fSL "http://www-us.apache.org/dist/kafka/${KAFKA_VERSION}/kafka_${SCALA_VERSION}-${KAFKA_VERSION}.tgz" -o kafka_${SCALA_VERSION}-${KAFKA_VERSION}.tgz \
     && echo "${KAFKA_DOWNLOAD_SHA1}  kafka_${SCALA_VERSION}-${KAFKA_VERSION}.tgz" | sha1sum -c - \
     && tar xfz kafka_"$SCALA_VERSION"-"$KAFKA_VERSION".tgz -C /opt \
     && mv /opt/kafka_"$SCALA_VERSION"-"$KAFKA_VERSION" /opt/kafka \