[SPARK-2524] missing document about spark.deploy.retainedDrivers

https://issues.apache.org/jira/browse/SPARK-2524
The configuration on spark.deploy.retainedDrivers is undocumented but actually used
https://github.com/apache/spark/blob/master/core/src/main/scala/org/apache/spark/deploy/master/Master.scala#L60

Author: lianhuiwang <[email protected]>
Author: Wang Lianhui <[email protected]>
Author: unknown <[email protected]>

Closes apache#1443 from lianhuiwang/SPARK-2524 and squashes the following commits:

64660fd [Wang Lianhui] address pwendell's comments
5f6bbb7 [Wang Lianhui] missing document about spark.deploy.retainedDrivers
44a3f50 [unknown] Merge remote-tracking branch 'upstream/master'
eacf933 [lianhuiwang] Merge remote-tracking branch 'upstream/master'
8bbfe76 [lianhuiwang] Merge remote-tracking branch 'upstream/master'
480ce94 [lianhuiwang] address aarondav comments
f2b5970 [lianhuiwang] bugfix worker DriverStateChanged state should match DriverState.FAILED

Author: lianhuiwang

docs/spark-standalone.md

@@ -156,6 +156,20 @@ SPARK_MASTER_OPTS supports the following system properties:
 
 <table class="table">
 <tr><th>Property Name</th><th>Default</th><th>Meaning</th></tr>
+<tr>
+  <td><code>spark.deploy.retainedApplications</code></td>
+  <td>200</td>
+  <td>
+    The maximum number of completed applications to display. Older applications will be dropped from the UI to maintain this limit.<br/>
+  </td>
+</tr>
+<tr>
+  <td><code>spark.deploy.retainedDrivers</code></td>
+  <td>200</td>
+  <td>
+   The maximum number of completed drivers to display. Older drivers will be dropped from the UI to maintain this limit.<br/>
+  </td>
+</tr>
 <tr>
   <td><code>spark.deploy.spreadOut</code></td>
   <td>true</td>