AUTO-513: logging utcnow in ISO8601 format

Implemented utcisoformat() in utils/timestamp.py that gives ISO format of given time.
Also, improved the scheduler log bind test by mocking datetime and generate_transaction_id
Log formatter accomodates datetime and Failure objects

it converts datetime and failure objects into more readable format.
- Removed utcisoformat() function as we really dont know if a datetime is UTC.
- Reverted scheduler changes made by earlier commit
list of tuples instead of dict

since we are iterating anyways
pep8 fix
doc change and minor cleanup
Merge pull request #346 from rackerlabs/auto-513-datetime-log

AUTO-513: logging utcnow in ISO8601 format