[SPARK-11026] [YARN] spark.yarn.user.classpath.first does work for...

[SPARK-11026] [YARN] spark.yarn.user.classpath.first does work for 'spark-submit --jars hdfs://user/foo.jar'

when spark.yarn.user.classpath.first=true and using 'spark-submit --jars hdfs://user/foo.jar', it can not put foo.jar to system classpath. so we need to put yarn's linkNames of jars to the system classpath. vanzin tgravescs

Author: Lianhui Wang <lianhuiwang09@gmail.com>

Closes #9045 from lianhuiwang/spark-11026.