Improve the error message if accessing cluster during validation fails.

Author: varshavaradarajan

src/main/java/cd/go/contrib/elasticagent/executors/ValidateConfigurationExecutor.java

@@ -85,8 +85,12 @@ private void validateNamespaceExistence() {
 
             result.add(error(NAMESPACE.key(), format("Namespace `{0}` does not exist in you cluster. Run \"kubectl create namespace {1}\" to create a namespace.", namespace, namespace)));
         } catch (Exception e) {
-            LOG.error(format("Failed to validate namespace existence: {0} Please check plugin log for more detail.", namespace), e);
-            result.add(error(NAMESPACE.key(), format("Failed to validate namespace existence: {0} Please check plugin log for more detail.", namespace)));
+            String message = "Failed validation of plugin settings. The reasons could be - " +
+                    "Cluster Url is configured incorrectly or " +
+                    "the service account token might not have enough permissions to list namespaces or " +
+                    "incorrect CA certificate.";
+            LOG.error(message, e);
+            result.add(error(NAMESPACE.key(), format(message + "Please check the plugin log for more details.")));
         }
     }