[SPARK-26685][K8S] Correct placement of ARG declaration

Latest Docker releases are stricter in their enforcement of build argument scope.  The location of the `ARG spark_uid` declaration in the Python and R Dockerfiles means the variable is out of scope by the time it is used in a `USER` declaration resulting in a container running as root rather than the default/configured UID.

Also with some of the refactoring of the script that has happened since my PR that introduced the configurable UID it turns out the `-u <uid>` argument is not being properly passed to the Python and R image builds when those are opted into

## What changes were proposed in this pull request?

This commit moves the `ARG` declaration to just before the argument is used such that it is in scope.  It also ensures that Python and R image builds receive the build arguments that include the `spark_uid` argument where relevant

## How was this patch tested?

Prior to the patch images are produced where the Python and R images ignore the default/configured UID:

```
> docker run -it --entrypoint /bin/bash rvesse/spark-py:uid456
bash-4.4# whoami
root
bash-4.4# id -u
0
bash-4.4# exit
> docker run -it --entrypoint /bin/bash rvesse/spark:uid456
bash-4.4$ id -u
456
bash-4.4$ exit
```

Note that the Python image is still running as `root` having ignored the configured UID of 456 while the base image has the correct UID because the relevant `ARG` declaration is correctly in scope.

After the patch the correct UID is observed:

```
> docker run -it --entrypoint /bin/bash rvesse/spark-r:uid456
bash-4.4$ id -u
456
bash-4.4$ exit
exit
> docker run -it --entrypoint /bin/bash rvesse/spark-py:uid456
bash-4.4$ id -u
456
bash-4.4$ exit
exit
> docker run -it --entrypoint /bin/bash rvesse/spark:uid456
bash-4.4$ id -u
456
bash-4.4$ exit
```

Closes apache#23611 from rvesse/SPARK-26685.

Authored-by: Rob Vesse <[email protected]>
Signed-off-by: Marcelo Vanzin <[email protected]>

bin/docker-image-tool.sh

@@ -154,10 +154,11 @@ function build {
   fi
 
   local BINDING_BUILD_ARGS=(
-    ${BUILD_PARAMS}
+    ${BUILD_ARGS[@]}
     --build-arg
     base_img=$(image_ref spark)
   )
+
   local BASEDOCKERFILE=${BASEDOCKERFILE:-"kubernetes/dockerfiles/spark/Dockerfile"}
   local PYDOCKERFILE=${PYDOCKERFILE:-false}
   local RDOCKERFILE=${RDOCKERFILE:-false}

resource-managers/kubernetes/docker/src/main/dockerfiles/spark/bindings/R/Dockerfile

@@ -16,7 +16,6 @@
 #
 
 ARG base_img
-ARG spark_uid=185
 
 FROM $base_img
 WORKDIR /
@@ -35,4 +34,5 @@ WORKDIR /opt/spark/work-dir
 ENTRYPOINT [ "/opt/entrypoint.sh" ]
 
 # Specify the User that the actual main process will run as
+ARG spark_uid=185
 USER ${spark_uid}

resource-managers/kubernetes/docker/src/main/dockerfiles/spark/bindings/python/Dockerfile

@@ -16,7 +16,6 @@
 #
 
 ARG base_img
-ARG spark_uid=185
 
 FROM $base_img
 WORKDIR /
@@ -46,4 +45,5 @@ WORKDIR /opt/spark/work-dir
 ENTRYPOINT [ "/opt/entrypoint.sh" ]
 
 # Specify the User that the actual main process will run as
+ARG spark_uid=185
 USER ${spark_uid}