[SPARK-1720][SPARK-1719] use LD_LIBRARY_PATH instead of -Djava.library.path

- [X] Standalone
- [X] YARN
- [X] Mesos
- [X]  Mac OS X
- [X] Linux
- [ ]  Windows

This is another implementation about #1031

Author: GuoQiang Li <witgo@qq.com>

Closes #2711 from witgo/SPARK-1719 and squashes the following commits:

c7b26f6 [GuoQiang Li] review commits
4488e41 [GuoQiang Li] Refactoring CommandUtils
a444094 [GuoQiang Li] review commits
40c0b4a [GuoQiang Li] Add buildLocalCommand method
c1a0ddd [GuoQiang Li] fix comments
156ce88 [GuoQiang Li] review commit
38aa377 [GuoQiang Li] Refactor CommandUtils.scala
4269e00 [GuoQiang Li] Refactor SparkSubmitDriverBootstrapper.scala
7a1d634 [GuoQiang Li] use LD_LIBRARY_PATH instead of -Djava.library.path
[SPARK-4102] Remove unused ShuffleReader.stop() method.

This method is not implemented by the only subclass
(HashShuffleReader), nor is it ever called. While the
use of Scala's fancy "???" was pretty exciting, the method's
existence can only lead to confusion and it therefore should
be deleted.

mateiz was there a reason for adding this that I'm
missing?

Author: Kay Ousterhout <kayousterhout@gmail.com>

Closes #2966 from kayousterhout/SPARK-4102 and squashes the following commits:

532c564 [Kay Ousterhout] Added back commented-out method, as per Matei's request
904655e [Kay Ousterhout] [SPARK-4102] Remove unused ShuffleReader.stop() method.
[SPARK-4130][MLlib] Fixing libSVM parser bug with extra whitespace

This simple patch filters out extra whitespace entries.

Author: Joseph E. Gonzalez <joseph.e.gonzalez@gmail.com>
Author: Joey <joseph.e.gonzalez@gmail.com>

Closes #2996 from jegonzal/loadLibSVM and squashes the following commits:

e0227ab [Joey] improving readability
e028e84 [Joseph E. Gonzalez] fixing whitespace bug in loadLibSVMFile when parsing libSVM files