ZEPPELIN-773 update doc for know issue, and more error logging

docs/interpreter/livy.md

@@ -85,3 +85,9 @@ You can leverage [Zeppelin Dynamic Form]({{BASE_PATH}}/manual/dynamicform.html).
 %livy.pyspark
 print "${group_by=product_id,product_id|product_name|customer_id|store_id}"
 ```
+
+## Know Issue
+If you are getting an error `Blacklisted configuration values in session config: spark.master`
+
+edit `conf/spark-blacklist.conf` file in livy server and comment out `#spark.master` line.
+

livy/src/main/java/org/apache/zeppelin/livy/LivyHelper.java

@@ -367,6 +367,7 @@ public class LivyHelper {
       if (responseString.contains("CreateInteractiveRequest[\\\"master\\\"]")) {
         return responseString;
       }
+      LOGGER.error("Error with 500 StatusCode: ", responseString);
     }
     return null;
   }