feat(testing): be a little more verbose about ZK download URL

So that we understand better when it fails

ensure-zookeeper-env.sh

@@ -14,7 +14,9 @@ ZOO_MIRROR_URL="http://archive.apache.org/dist"
 function download_zookeeper(){
     mkdir -p $ZOO_BASE_DIR
     cd $ZOO_BASE_DIR
-    curl --silent -C - $ZOO_MIRROR_URL/zookeeper/zookeeper-$ZOOKEEPER_VERSION/${ZOOKEEPER_PREFIX}zookeeper-${ZOOKEEPER_VERSION}${ZOOKEEPER_SUFFIX}.tar.gz | tar -zx
+    ZOOKEEPER_DOWNLOAD_URL=${ZOO_MIRROR_URL}/zookeeper/zookeeper-${ZOOKEEPER_VERSION}/${ZOOKEEPER_PREFIX}zookeeper-${ZOOKEEPER_VERSION}${ZOOKEEPER_SUFFIX}.tar.gz
+    echo "Will download ZK from ${ZOOKEEPER_DOWNLOAD_URL}"
+    (curl --silent -C - $ZOOKEEPER_DOWNLOAD_URL | tar -zx) || echo "Failed downloading ZK from ${ZOOKEEPER_DOWNLOAD_URL}"
     mv ${ZOOKEEPER_PREFIX}zookeeper-${ZOOKEEPER_VERSION}${ZOOKEEPER_SUFFIX} $ZOOKEEPER_VERSION
     chmod a+x $ZOOKEEPER_PATH/bin/zkServer.sh
 }