[SPARK-25803][K8S] Fix docker-image-tool.sh -n option
[SPARK-25803][K8S] Fix docker-image-tool.sh -n option

## What changes were proposed in this pull request?

docker-image-tool.sh uses getopts in which a colon signifies that an
option takes an argument.  Since -n does not take an argument it
should not have a colon.

## How was this patch tested?

Following the reproduction in [JIRA](https://issues.apache.org/jira/browse/SPARK-25803):-

0. Created a custom Dockerfile to use for the spark-r container image.
In each of the steps below the path to this Dockerfile is passed with the '-R' option.
(spark-r is used here simply as an example, the bug applies to all options)

1. Built container images without '-n'.
The [result](https://gist.github.com/sel/59f0911bb1a6a485c2487cf7ca770f9d) is that the '-R' option is honoured and the hello-world image is built for spark-r, as expected.

2. Built container images with '-n' to reproduce the issue
The [result](https://gist.github.com/sel/e5cabb9f3bdad5d087349e7fbed75141) is that the '-R' option is ignored and the default container image for spark-r is built

3. Applied the patch and re-built container images with '-n' and did not reproduce the issue
The [result](https://gist.github.com/sel/6af14b95012ba8ff267a4fce6e3bd3bf) is that the '-R' option is honoured and the hello-world image is built for spark-r, as expected.

Closes #22798 from sel/fix-docker-image-tool-nocache.

Authored-by: Steve <c7c752379a2f5bcc583bb9f942c2c8134cd3678a@users.noreply.github.com>
Signed-off-by: Marcelo Vanzin <8283fd24ce58e0bb0d6bf349e9064fef42c4d84e@cloudera.com>

bdrillard/spark,dongjoon-hyun/spark,taroplus/spark,yanboliang/spark,yanboliang/spark,Aegeaner/spark,maropu/spark,highfei2011/spark,dbtsai/spark,ptkool/spark,apache/spark,vinodkc/spark,facaiy/spark,jiangxb1987/spark,BryanCutler/spark,rednaxelafx/apache-spark,rezasafi/spark,kevinyu98/spark,WindCanDie/spark,goldmedal/spark,wangmiao1981/spark,bdrillard/spark,aosagie/spark,jkbradley/spark,holdenk/spark,goldmedal/spark,gengliangwang/spark,WindCanDie/spark,Aegeaner/spark,witgo/spark,caneGuy/spark,wangmiao1981/spark,xuanyuanking/spark,kiszk/spark,xuanyuanking/spark,kevinyu98/spark,ptkool/spark,dongjoon-hyun/spark,zuotingbing/spark,milliman/spark,mdespriee/spark,mahak/spark,Aegeaner/spark,ueshin/apache-spark,maropu/spark,gengliangwang/spark,ueshin/apache-spark,icexelloss/spark,gengliangwang/spark,pgandhi999/spark,hvanhovell/spark,vinodkc/spark,nchammas/spark,ConeyLiu/spark,highfei2011/spark,bdrillard/spark,shaneknapp/spark,taroplus/spark,dbtsai/spark,ueshin/apache-spark,nchammas/spark,chuckchen/spark,LantaoJin/spark,JoshRosen/spark,WeichenXu123/spark,taroplus/spark,actuaryzhang/spark,ahnqirage/spark,nchammas/spark,zero323/spark,chuckchen/spark,hhbyyh/spark,BryanCutler/spark,jkbradley/spark,highfei2011/spark,cloud-fan/spark,kiszk/spark,mdespriee/spark,shuangshuangwang/spark,vinodkc/spark,wangyum/spark,hvanhovell/spark,hvanhovell/spark,milliman/spark,maropu/spark,shuangshuangwang/spark,srowen/spark,HyukjinKwon/spark,facaiy/spark,wzhfy/spark,jkbradley/spark,wzhfy/spark,Aegeaner/spark,dongjoon-hyun/spark,WeichenXu123/spark,yanboliang/spark,actuaryzhang/spark,dbtsai/spark,goldmedal/spark,darionyaphet/spark,wangyum/spark,zzcclp/spark,vinodkc/spark,wzhfy/spark,ConeyLiu/spark,zuotingbing/spark,gengliangwang/spark,caneGuy/spark,jiangxb1987/spark,BryanCutler/spark,wangyum/spark,caneGuy/spark,srowen/spark,ConeyLiu/spark,rednaxelafx/apache-spark,wangmiao1981/spark,maropu/spark,jiangxb1987/spark,holdenk/spark,nchammas/spark,srowen/spark,spark-test/spark,witgo/spark,dongjoon-hyun/spark,vinodkc/spark,apache/spark,xuanyuanking/spark,zuotingbing/spark,spark-test/spark,ConeyLiu/spark,zuotingbing/spark,jiangxb1987/spark,skonto/spark,matthewfranglen/spark,cloud-fan/spark,ptkool/spark,zuotingbing/spark,facaiy/spark,xuanyuanking/spark,mahak/spark,WeichenXu123/spark,icexelloss/spark,dbtsai/spark,actuaryzhang/spark,rednaxelafx/apache-spark,mdespriee/spark,cloud-fan/spark,vinodkc/spark,LantaoJin/spark,LantaoJin/spark,bdrillard/spark,rezasafi/spark,kiszk/spark,wzhfy/spark,zero323/spark,xuanyuanking/spark,JoshRosen/spark,zzcclp/spark,actuaryzhang/spark,bdrillard/spark,shuangshuangwang/spark,srowen/spark,xuanyuanking/spark,icexelloss/spark,gengliangwang/spark,JoshRosen/spark,spark-test/spark,rezasafi/spark,zzcclp/spark,wangyum/spark,wangyum/spark,WindCanDie/spark,JoshRosen/spark,holdenk/spark,yanboliang/spark,shuangshuangwang/spark,spark-test/spark,kevinyu98/spark,hhbyyh/spark,jiangxb1987/spark,guoxiaolongzte/spark,witgo/spark,WindCanDie/spark,apache/spark,kiszk/spark,zero323/spark,LantaoJin/spark,wzhfy/spark,techaddict/spark,pgandhi999/spark,ptkool/spark,chuckchen/spark,pgandhi999/spark,zuotingbing/spark,wangyum/spark,jkbradley/spark,WindCanDie/spark,goldmedal/spark,Aegeaner/spark,BryanCutler/spark,milliman/spark,spark-test/spark,ahnqirage/spark,chuckchen/spark,chuckchen/spark,srowen/spark,aosagie/spark,caneGuy/spark,HyukjinKwon/spark,shuangshuangwang/spark,BryanCutler/spark,kevinyu98/spark,ueshin/apache-spark,rezasafi/spark,techaddict/spark,srowen/spark,jkbradley/spark,icexelloss/spark,nchammas/spark,pgandhi999/spark,guoxiaolongzte/spark,maropu/spark,dbtsai/spark,pgandhi999/spark,zzcclp/spark,ahnqirage/spark,cloud-fan/spark,BryanCutler/spark,jiangxb1987/spark,darionyaphet/spark,guoxiaolongzte/spark,LantaoJin/spark,chuckchen/spark,spark-test/spark,icexelloss/spark,pgandhi999/spark,maropu/spark,aosagie/spark,aosagie/spark,wzhfy/spark,darionyaphet/spark,ConeyLiu/spark,icexelloss/spark,actuaryzhang/spark,shaneknapp/spark,BryanCutler/spark,highfei2011/spark,holdenk/spark,taroplus/spark,zzcclp/spark,aosagie/spark,ueshin/apache-spark,shaneknapp/spark,mdespriee/spark,jkbradley/spark,mahak/spark,ConeyLiu/spark,chuckchen/spark,ConeyLiu/spark,guoxiaolongzte/spark,srowen/spark,shaneknapp/spark,hvanhovell/spark,rednaxelafx/apache-spark,goldmedal/spark,dongjoon-hyun/spark,hhbyyh/spark,kiszk/spark,aosagie/spark,actuaryzhang/spark,HyukjinKwon/spark,skonto/spark,WeichenXu123/spark,HyukjinKwon/spark,dbtsai/spark,witgo/spark,highfei2011/spark,HyukjinKwon/spark,bdrillard/spark,caneGuy/spark,taroplus/spark,darionyaphet/spark,ahnqirage/spark,icexelloss/spark,wangyum/spark,aosagie/spark,pgandhi999/spark,gengliangwang/spark,jkbradley/spark,goldmedal/spark,shuangshuangwang/spark,wangmiao1981/spark,ahnqirage/spark,milliman/spark,witgo/spark,holdenk/spark,guoxiaolongzte/spark,shuangshuangwang/spark,witgo/spark,taroplus/spark,cloud-fan/spark,LantaoJin/spark,hhbyyh/spark,milliman/spark,darionyaphet/spark,facaiy/spark,mdespriee/spark,rezasafi/spark,techaddict/spark,tarop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