[SPARK-5376][Mesos] MesosExecutor should have correct resources

- changed term from `cpus` to `cores`
- Reworded docs

core/src/main/scala/org/apache/spark/scheduler/cluster/mesos/MesosSchedulerBackend.scala

@@ -68,7 +68,7 @@ private[spark] class MesosSchedulerBackend(
   // The listener bus to publish executor added/removed events.
   val listenerBus = sc.listenerBus
 
-  val executorCpus = sc.conf.getInt("spark.mesos.executor.cpus", 1)
+  val executorCpus = sc.conf.getInt("spark.mesos.executor.cores", 1)
 
   @volatile var appId: String = _
 

docs/configuration.md

@@ -342,10 +342,10 @@ Apart from these, the following properties are also available, and may be useful
   </td>
 </tr>
 <tr>
-  <td><code>spark.mesos.executor.cpus</code></td>
+  <td><code>spark.mesos.executor.cores</code></td>
   <td>1</td>
   <td>
-    This value is the amount of cores so that executor is running itself.
+    The amount of cores to request for running the mesos executor.
   </td>
 </tr>
 </table>

docs/running-on-mesos.md

@@ -227,10 +227,10 @@ See the [configuration page](configuration.html) for information on Spark config
   </td>
 </tr>
 <tr>
-  <td><code>spark.mesos.executor.cpus</code></td>
+  <td><code>spark.mesos.executor.cores</code></td>
   <td>1</td>
   <td>
-    The amount of cores that Mesos executor will request additionally for running executor itself.
+    The amount of cores to request for running the mesos executor.
   </td>
 </tr>
 </table>