Change the order of CLASSPATH.
Merge pull request #275 from ueshin/wip/changeclasspathorder

Change the order of CLASSPATH.

SPARK_TOOLS_JAR should be placed after CLASSPATH or at least after
SPARK_CLASSPATH.

If SPARK_TOOLS_JAR is placed before CLASSPATH, all assembled classes and
resources in spark-tools-assembly.jar beat those in CLASSPATH or
SPARK_CLASSPATH, which might be replaced by customized versions.