initial prototype to get task status using celery
merging resource reservation branch and resolving conflicts
added task status db model, manager and handlers in Task class to update task statuses
added docstrings to task's status update handlers
Some cleanup, minor fixes and doc corrections
adding unit tests for task_status_manager
adding task status and handler unit tests
fixing DuplicateKeyError raised by pymongo in case of existing task status
fixing consumer controller unit tests
incorporating PR review feedback
adding/updating task statuses using 'upsert' to avoid race condition
updated task __call__ and handlers to update task status only when async task is run
few minor unit test updates
Incorporating PR review feedback
incorporating some more PR feedback and adding/updating unit tests
added test for getting list of tasks through dispatch controller
few more minor updates
Merge pull request #694 from pulp/skarmark-distributed-tasks

Skarmark distributed tasks status tracking