Improved timestamp parsing

Use dateutil to accept be more flexible in parsing timestamps. A recent
upgrade to ElasticSearch changed the timestamp format to use '+00:00' to
note the timezone instead of 'Z'

Co-Authored-By: Joe Gordon <joe.gordon0@gmail.com>
Change-Id: I11f441ba3bf7ba46c55921352fcc87eb5d1ce3ae
Merge "Improved timestamp parsing"