Add label support for kubectl describe

Add -l option to kubectl describe command, allow it return
multiple results filtered by label selector.

docs/kubectl_describe.md

@@ -22,12 +22,16 @@ $ kubectl describe nodes kubernetes-minion-emt8.c.myproject.internal
 
 // Describe a pod
 $ kubectl describe pods/nginx
+
+// Describe pods by label name=myLabel
+$ kubectl describe po -l name=myLabel
 ```
 
 ### Options
 
 ```
   -h, --help=false: help for describe
+  -l, --selector="": Selector (label query) to filter on
 ```
 
 ### Options inherited from parent commands
@@ -62,6 +66,6 @@ $ kubectl describe pods/nginx
 ### SEE ALSO
 * [kubectl](kubectl.md)	 - kubectl controls the Kubernetes cluster manager
 
-###### Auto generated by spf13/cobra at 2015-05-21 10:33:11.177122438 +0000 UTC
+###### Auto generated by spf13/cobra at 2015-06-12 06:44:05.105790085 +0000 UTC
 
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