[SPARK-3677] [BUILD] [YARN] pom.xml and SparkBuild.scala are wrong : Scalastyle is never applied to the sources under yarn/common

When we run "sbt -Pyarn scalastyle" or "mvn package", scalastyle is not applied to the sources under yarn/common.
@ScrapCodes If we remove settings for alpha and stable from SparkBuild.scala, we fail to build with 'sbt/sbt -Pyarn -Phadoop-2.2 assembly' even though it can pass scalastyle.