Extract entrypoint command from bin scripts, try native-image zookeeper

[solsson]

Use the command generated by Kafka's ./bin/*.sh as entrypoints. Given the same env these scripts simply produce the same command every time, and append args. See #309 and https://github.com/solsson/dockerfiles/blob/master/hooks/build.

Now things like #306 should be done with --override.

[solsson]

I had a very strange init error that isn't reproducible: the symlink operation failed, complaining that the target path exists.

+ '[' '!' -d /var/lib/zookeeper/data ']'
+ '[' -z 1 ']'
+ export ZOOKEEPER_SERVER_ID=2
+ ZOOKEEPER_SERVER_ID=2
+ echo 2
+ tee /var/lib/zookeeper/data/myid
2
+ cp -Lur /etc/kafka-configmap/init.sh /etc/kafka-configmap/log4j.properties /etc/kafka-configmap/zookeeper.properties /etc/kafka/
+ '[' '!' -z 0 ']'
+ '[' '!' -z 3 ']'
+ sed -i 's/^server\./#server./' /etc/kafka/zookeeper.properties
++ seq 0
++ seq 3
+ for N in $(seq $(( $REPLICAS - $PZOO_REPLICAS )))
+ echo server.1=zoo-0.zoo:2888:3888:participant
+ for N in $(seq $(( $REPLICAS - $PZOO_REPLICAS )))
+ echo server.2=zoo-1.zoo:2888:3888:participant
+ for N in $(seq $(( $REPLICAS - $PZOO_REPLICAS )))
+ echo server.3=zoo-2.zoo:2888:3888:participant
+ sed -i 's/server\.2\=[a-z0-9.-]*/server.2=0.0.0.0/' /etc/kafka/zookeeper.properties
+ ln -s /etc/kafka/zookeeper.properties /etc/kafka/zookeeper.properties.scale-3.zoo-1
ln: failed to create symbolic link '/etc/kafka/zookeeper.properties.scale-3.zoo-1': File exists

After delete pod the next pod came up as usual.

[solsson]

To summarize changes from [v6.0.4]():

The ambition was to keep the base folders kafka and zookeeper unchanged, but we had to do some changes to init scripts and container args in order to support an updated nonroot base and the new native base.

• Kafka 2.5.0
• Zookeeper 3.5.8
• Experimental GraalVM native-image binary build of Zookeeper 3.5.8
• Variants scale-1 and dev-small use native zookeeper because faster zk startup time means fewer broker crashloops and thus reduced resource waste when provisioning dev/CI clusters.
• The REPLICAS environment variable is new. It replaces ZOO_REPLICAS while PZOO_REPLICAS remains.
• The .properties file paths written by init-config scripts now contain pod names so config can, if desired, vary per pod. There's symlinks to the original path to avoid breaking existing container command/args.
• Zookeeper .properties files also contain the replicas number because they must enumerate all peers and thus need to be changed at zookeeper scaling up or down.