[SPARK-25036][SQL][FOLLOW-UP] Avoid match may not be exhaustive in Scala-2.12.

[kiszk]

What changes were proposed in this pull request?

This is a follow-up pr of #22014 and #22039

We still have some more compilation errors in mllib with scala-2.12 with sbt:

[error] [warn] /home/ishizaki/Spark/PR/scala212/spark/mllib/src/main/scala/org/apache/spark/ml/evaluation/ClusteringEvaluator.scala:116: match may not be exhaustive.
[error] It would fail on the following inputs: ("silhouette", _), (_, "cosine"), (_, "squaredEuclidean"), (_, String()), (_, _)
[error] [warn]     ($(metricName), $(distanceMeasure)) match {
[error] [warn] 

How was this patch tested?

Existing UTs

[kiszk]

cc @ueshin @srowen @HyukjinKwon

[srowen]

I see, did you run sbt one more time after this to see if there were more? would be good to address all of the ones worth changing in this pass.

[SparkQA]

Test build #94509 has finished for PR 22058 at commit 5655d83.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[srowen]

This is OK, but doesn't really add much beyond what the MatchError would have said. Worth a message like "No support for metric $mn, distance $dm"?

[kiszk]

I think that this is the last one with the following command. With a pair of this PR and #22059, I succeeded to run sbt. But, I would like to confirm this with @ueshin.

build/sbt -Pscala-2.12 -Phadoop-2.6 -Pkubernetes -Phive -Pmesos -Phive-thriftserver -Pflume -Pkinesis-asl -Pyarn package

[SparkQA]

Test build #94517 has finished for PR 22058 at commit 3084b55.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[srowen]

Merged to master