SPARK-2400 : fix spark.yarn.max.executor.failures explaination

According to
```scala
  private val maxNumExecutorFailures = sparkConf.getInt("spark.yarn.max.executor.failures",
    sparkConf.getInt("spark.yarn.max.worker.failures", math.max(args.numExecutors * 2, 3)))
```
default value should be numExecutors * 2, with minimum of 3,  and it's same to the config
`spark.yarn.max.worker.failures`

Author: CrazyJvm <crazyjvm@gmail.com>

Closes #1282 from CrazyJvm/yarn-doc and squashes the following commits:

1a5f25b [CrazyJvm] remove deprecated config
c438aec [CrazyJvm] fix style
86effa6 [CrazyJvm] change expression
211f130 [CrazyJvm] fix html tag
2900d23 [CrazyJvm] fix style
a4b2e27 [CrazyJvm] fix configuration spark.yarn.max.executor.failures