Secret parameter validation added

Author: maxkochubey

lib/fluent/plugin/out_azure-storage-append-blob.rb

@@ -57,6 +57,10 @@ def configure(conf)
         if @azure_container.nil?
           raise ConfigError, 'azure_container is needed'
         end
+
+        if @azure_storage_access_key.nil? || @azure_storage_sas_token.nil?
+          raise ConfigError, "either 'azure_storage_access_key' or 'azure_storage_sas_token' parameter must be provided"
+        end
       end
 
       def multi_workers_ready?