Return a timedelta for this build.

        Measure the time between this build's start and end time, or "now"
        if the build has not yet finished.

        :returns: timedelta object

def duration(self):
        """
        Return a timedelta for this build.

        Measure the time between this build's start and end time, or "now"
        if the build has not yet finished.

        :returns: timedelta object
        """
        if self.completion_ts:
            end = self.completed
        else:
            end = datetime.utcnow()
        return end - self.started