Eliminate blocking call to scheduler for isguaranteed

LlapTaskCommunicator requires isGuaranteed information from LlapTaskScheduler just before sending the actual request to the executor. There is no particular ordering between the writing the submit request to the network and scheduler decisions. Therefore, we can just put the initial isGuaranteed information in task allocation rather than calling back scheduler.

Depends on https://jira.apache.org/jira/browse/TEZ-4192