[SPARK-1522]: YARN ClientBase throws a NPE if there is no YARN Application specific CP

* `ClientBase` Object now extends `Logger`
* `getDefaultYarnApplicationClasspath` and `getDefaultMRApplicationClasspath`
    * Now return `Option[Seq[String]]` instead of `Try[Array[String]]`
    * Don't attempt to catch `NoSuchFieldError`, its a linkage error and can't
      happen in this context since the class as well as the field are
      accessed using reflection.
    * Either log the error in case `Try` fails else log a debug message.

[ticket: SPARK-1522] : https://issues.apache.org/jira/browse/SPARK-1522

Author      : berngp
Reviewer    : andrewor14, tgravescs
Testing     : ?