Add option for adding connectors jar file.

[awakelee]

I found that there are some wget commands in Dockerfile. Maybe we can provide user some options to add jars without learning writing Dockerfile.

[mirkof]

You can just manually copy flink jars to docker, without changing anything. ie.

Copy the jars I want

SQL_CLIENT_CONTAINER_ID=$(docker ps -qf "name=sql-client")
docker cp /myjars $SQL_CLIENT_CONTAINER_ID:/tmp/jars

Now copy all the jars to both sql-client and flink

cp /tmp/jars/*.jar /opt/flink/lib/.
cp /tmp/jars/*.jar /opt/sql-client/lib/.
./sql-client.sh