[SPARK-2742][yarn] delete useless variables

Author: XuTingjun <1039320815@qq.com>

Closes #1614 from XuTingjun/yarn-bug and squashes the following commits:

f07096e [XuTingjun] Update ClientArguments.scala
Link to Contributing to Spark wiki page on README.md.
[SPARK-3169] Removed dependency on spark streaming test from spark flume sink

Due to maven bug https://jira.codehaus.org/browse/MNG-1378, maven could not resolve spark streaming classes required by the spark-streaming test-jar dependency of external/flume-sink. There is no particular reason that the external/flume-sink has to depend on Spark Streaming at all, so I am eliminating this dependency. Also I have removed the exclusions present in the Flume dependencies, as there is no reason to exclude them (they were excluded in the external/flume module to prevent dependency collisions with Spark).

Since Jenkins will test the sbt build and the unit test, I only tested maven compilation locally.

Author: Tathagata Das <tathagata.das1565@gmail.com>

Closes #2101 from tdas/spark-sink-pom-fix and squashes the following commits:

8f42621 [Tathagata Das] Added Flume sink exclusions back, and added netty to test dependencies
93b559f [Tathagata Das] Removed dependency on spark streaming test from spark flume sink
[SPARK-2963] REGRESSION - The description about how to build for using CLI and Thrift JDBC server is absent in proper document  -

The most important things I mentioned in #1885 is as follows.

* People who build Spark is not always programmer.
* If a person who build Spark is not a programmer, he/she won't read programmer's guide before building.

So, how to build for using CLI and JDBC server is not only in programmer's guide.

Author: Kousuke Saruta <sarutak@oss.nttdata.co.jp>

Closes #2080 from sarutak/SPARK-2963 and squashes the following commits:

ee07c76 [Kousuke Saruta] Modified regression of the description about building for using Thrift JDBC server and CLI
ed53329 [Kousuke Saruta] Modified description and notaton of proper noun
07c59fc [Kousuke Saruta] Added a description about how to build to use HiveServer and CLI for SparkSQL to building-with-maven.md
6e6645a [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into SPARK-2963
c88fa93 [Kousuke Saruta] Added a description about building to use HiveServer and CLI for SparkSQL
[SPARK-2608] fix executor backend launch commond over mesos mode
Use SPARK_HOME for finding computing class path