update for polling support
Add ability for tasks to add sub-tasks to the polling list.  Also update the PulpCodedException to use keywords for the error fields.
Merge branch 'distributed-tasks' into barnabycourt-polling
Fix base class for integration tests so that it does not require queues to be up and running
Respond to PR comments
Merge pull request #763 from pulp/barnabycourt-polling

Update for task polling, nodes errors & PulpCodedException arguments