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/tests/functional/K8S_SystemTest.robot b/tests/functional/K8S_SystemTest.robot
index ba14607..47d2b2b 100644
--- a/tests/functional/K8S_SystemTest.robot
+++ b/tests/functional/K8S_SystemTest.robot
@@ -98,7 +98,7 @@
     [Documentation]    Get the number of configured ETCD nodes
     ${rc}    ${size}=    Run and Return Rc and Output
     ...    kubectl -n ${namespace} get ${ETCD_resources} ${ETCD_name} -o jsonpath='{.status.replicas}'
-    Should Be Equal As Integers    ${rc}    0
+    Should Be Equal As Integers    ${rc}    0   Could not get ETCD replica count
     [Return]    ${size}
 
 Scale ETCD
@@ -106,16 +106,16 @@
     [Documentation]    Scale down the number of ETCD pod
     ${rc}=    Run and Return Rc
     ...    kubectl -n ${namespace} patch ${ETCD_resources} ${ETCD_name} -p '{"spec":{"replicas": ${size}}}'
-    Should Be Equal As Integers    ${rc}    0
+    Should Be Equal As Integers    ${rc}    0   Could not scale ETCD
 
 Validate ETCD Size
     [Arguments]    ${namespace}    ${ETCD_cluster_size}
     [Documentation]    Scale down the number of ETCD pod
     ${rc}    ${size}=    Run and Return Rc and Output
     ...    kubectl -n ${namespace} get ${ETCD_resources} ${ETCD_name} -o jsonpath='{.status.replicas}'
-    Should Be Equal As Integers    ${rc}    0
+    Should Be Equal As Integers    ${rc}    0   Could not get ETCD replica count
     Should Be Equal As Integers    ${size}    ${ETCD_cluster_size}    Unexpected number of replicas
     ${rc}    ${size}=    Run and Return Rc and Output
     ...    kubectl -n ${namespace} get ${ETCD_resources} ${ETCD_name} -o jsonpath='{.status.readyReplicas}'
-    Should Be Equal As Integers    ${rc}    0
+    Should Be Equal As Integers    ${rc}    0   Could not get ETC ready replica count
     Should Be Equal As Integers    ${size}    ${ETCD_cluster_size}    Unexpected number of ready replicas