Correct DAG for updating the last.repl.id for a database during bootstrap load

We update the last.repl.id as a database property. This is done after all the bootstrap tasks to load the relevant data are done and is the last task to be run. however we are currently not setting up the DAG correctly for this task. This is getting added as the root task for now where as it should be the last task to be run in a DAG. This becomes more important after the inclusion of
HIVE-17426 since this will lead to parallel execution and incorrect DAG's will lead to incorrect results/state of the system.