[SPARK-1780] Non-existent SPARK_DAEMON_OPTS is lurking around

What they really mean is SPARK_DAEMON_***JAVA***_OPTS

Author: Andrew Or <andrewor14@gmail.com>

Closes #751 from andrewor14/spark-daemon-opts and squashes the following commits:

70c41f9 [Andrew Or] SPARK_DAEMON_OPTS -> SPARK_DAEMON_JAVA_OPTS
(cherry picked from commit ba96bb3d591130075763706526f86fb2aaffa3ae)

Signed-off-by: Patrick Wendell <pwendell@gmail.com>