Do not use six's text_type but string_types
normalize dates to use UTC timezone

Nova expects the UTC timezone as default, therefore we should normalize
all data to that timezone. Also, some API calls do no expect a TZ in the
request, so we have to remove the timezone info from the dates passed to
nova.
fix SSM messenger without records

When we have no records we were generating empty messages. This fix
checks if there are records before sending the message to the queue.