Increase the number of parallel tasks sent to daemons from am

The number of inflight tasks from AM to a single executor is hardcoded to 1 currently(https://github.com/apache/hive/blob/master/llap-client/src/java/org/apache/hadoop/hive/llap/tez/LlapProtocolClientProxy.java#L57 ). It does not make sense to increase this right now as communication between am and daemons happen synchronously anyway. After resolving https://issues.apache.org/jira/browse/HIVE-23746 this must be increased to at least number of execution slots per daemon.