[SPARK-2098] All Spark processes should support spark-defaults.conf, config file

This is another implementation about #1256
cc andrewor14 vanzin

Author: GuoQiang Li <witgo@qq.com>

Closes #2379 from witgo/SPARK-2098-new and squashes the following commits:

4ef1cbd [GuoQiang Li] review commit
49ef70e [GuoQiang Li] Refactor getDefaultPropertiesFile
c45d20c [GuoQiang Li] All Spark processes should support spark-defaults.conf, config file