[SPARK-6653][yarn] New configuration property to specify port for sparkYarnAM actor system

Author: shekhar.bansal

docs/running-on-yarn.md

@@ -133,6 +133,13 @@ Most of the configs are the same for Spark on YARN as for other deployment modes
     Same as <code>spark.yarn.driver.memoryOverhead</code>, but for the Application Master in client mode.
   </td>
 </tr>
+<tr>
+  <td><code>spark.yarn.am.port</code></td>
+  <td>(random)</td>
+  <td>
+    Port for the YARN Application Master to listen on.
+  </td>
+</tr>
 <tr>
   <td><code>spark.yarn.queue</code></td>
   <td>default</td>