[SPARK-2118] spark class should complain if tools jar is missing.

Author: Prashant Sharma <prashant.s@imaginea.com>

Closes #1068 from ScrapCodes/SPARK-2118/tools-jar-check and squashes the following commits:

29e768b [Prashant Sharma] Code Review
5cb6f7d [Prashant Sharma] [SPARK-2118] spark class should complaing if tools jar is missing.