[SPARK-33048][BUILD] Fix SparkBuild.scala to recognize build settings for Scala 2.13

[sarutak]

What changes were proposed in this pull request?

This PR fixes SparkBuild.scala to recognize build settings for Scala 2.13.
In SparkBuild.scala, a variable scalaBinaryVersion is hardcoded as 2.12.
So, an environment variable SPARK_SCALA_VERSION is also to be 2.12.
This issue causes some test suites (e.g. SparkSubmitSuite) to be error.

===== TEST OUTPUT FOR o.a.s.deploy.SparkSubmitSuite: 'user classpath first in driver' =====

20/10/02 08:55:30.234 redirect stderr for command /home/kou/work/oss/spark-scala-2.13/bin/spark-submit INFO Utils: Error: Could not find or load m
ain class org.apache.spark.launcher.Main
20/10/02 08:55:30.235 redirect stderr for command /home/kou/work/oss/spark-scala-2.13/bin/spark-submit INFO Utils: /home/kou/work/oss/spark-scala-
2.13/bin/spark-class: line 96: CMD: bad array subscript

The reason of this error is that environment variables SPARK_JARS_DIR and LAUNCH_CLASSPATH is defined in bin/spark-class as follows.

SPARK_JARS_DIR="${SPARK_HOME}/assembly/target/scala-$SPARK_SCALA_VERSION/jars"
LAUNCH_CLASSPATH="${SPARK_HOME}/launcher/target/scala-$SPARK_SCALA_VERSION/classes:$LAUNCH_CLASSPATH"

Why are the changes needed?

To build for Scala 2.13 successfully.

Does this PR introduce any user-facing change?

No.

How was this patch tested?

Tests for core module finish successfully.

build/sbt -Pscala-2.13 clean "core/test"

[SparkQA]

Kubernetes integration test starting
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/33937/

[SparkQA]

Kubernetes integration test status failure
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/33937/

[sarutak]

retest this please.

[SparkQA]

Kubernetes integration test starting
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/33943/

[SparkQA]

Kubernetes integration test status success
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/33943/

[SparkQA]

Test build #129324 has finished for PR 29927 at commit 833c2dd.

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

[SparkQA]

Test build #129332 has finished for PR 29927 at commit 833c2dd.

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

[HyukjinKwon]

cc @srowen FYI

[HyukjinKwon]

Merged to master.

[srowen]

Yep good call here.