Add more explicit console logging + minor fixes

* The checks with keywords such as "Should Not Be Empty", "Should
  Be Equal As"... should have a more explicit message on fail, so that
  the console output shows a clearer failing reason.
* Other minor fixes included in the commit are:
	* The Sadis file comparison to None string.
	* The KUBECTL_CONFIG variable not properly set, altough
	  apparently unused.

Change-Id: I9305ba791dd43c9088a7bcbcc9af568ae127f60f
diff --git a/libraries/k8s.robot b/libraries/k8s.robot
index c6fbc95..fa04d93 100755
--- a/libraries/k8s.robot
+++ b/libraries/k8s.robot
@@ -460,7 +460,7 @@
     FOR    ${I}    IN RANGE    0    ${lenght}
         ${output}=    Run
         ...    kubectl -n ${namespace} get pods -l ${key}=${value} -o=jsonpath="{.items[${I}].status.containerStatuses[].ready}"
-        Should Not Contain    ${output}    false
+        Should Not Contain    ${output}    false    All pods with label ${key}=${value} are not ready
     END
 
 Wait For Pods Ready