[SPARK-19810][BUILD][FOLLOW-UP] jcl-over-slf4j dependency needs to be compile scope for SBT build

## What changes were proposed in this pull request?

jcl-over-slf4j dependency needs to be compile scope for SBT build, to make it available for commons-logging dependents like Hadoop

#17150 (comment)
https://github.com/apache/spark/pull/17150/files#r128728089

## How was this patch tested?

Manual tests

Author: Sean Owen <sowen@cloudera.com>

Closes #18703 from srowen/SPARK-19810.2.

Author: srowen

pom.xml

@@ -510,7 +510,7 @@
         <groupId>org.slf4j</groupId>
         <artifactId>jcl-over-slf4j</artifactId>
         <version>${slf4j.version}</version>
-        <scope>runtime</scope>
+        <!-- runtime scope is appropriate, but causes SBT build problems -->
       </dependency>
       <dependency>
         <groupId>log4j</groupId>