[SPARK-4116][YARN]Delete the abandoned log4j-spark-container.properties

Since its name reduced at https://github.com/apache/spark/pull/560, the log4j-spark-container.properties was never used again.
And I have searched its name globally in code and found no cite.

Author: WangTaoTheTonic <barneystinson@aliyun.com>

Closes #2977 from WangTaoTheTonic/delLog4j and squashes the following commits:

fb2729f [WangTaoTheTonic] delete the log4j file obsoleted
[SPARK-4095][YARN][Minor]extract val isLaunchingDriver in ClientBase

Instead of checking if `args.userClass` is null repeatedly, we extract it to an global val as in `ApplicationMaster`.

Author: WangTaoTheTonic <barneystinson@aliyun.com>

Closes #2954 from WangTaoTheTonic/MemUnit and squashes the following commits:

13bda20 [WangTaoTheTonic] extract val isLaunchingDriver in ClientBase