trial tests log log_time should be human readable

[manishtomar]

Sample log from one of the test from running trial integration tests trial otter.integration.tests

Request to delete http://192.168.7.1:9000/v1.0/000001/groups/360b7103-c404-4e4c-9c63-2c0e63b21147?force=true starting.
{
  "url_params": null,
  "format": "%(log_legacy)s",
  "treq_request_id": "76cba289-69df-4809-aed8-cf61a6e279b8",
  "log_text": "Request to {method} {url} starting.",
  "log_legacy": "<twisted.logger._stdlib.StringifiableFromEvent object at 0x2ba85d0>",
  "log_time": 1480619234.565187,
  "log_namespace": "log_legacy",
  "log_level": "<LogLevel=info>",
  "level": 6,
  "url": "http://192.168.7.1:9000/v1.0/000001/groups/360b7103-c404-4e4c-9c63-2c0e63b21147?force=true",
  "system": "treq.request",
  "log_system": "treq.request",
  "time": 1480619234.565187,
  "log_format": "{log_text}",
  "method": "delete"
}

The log_time should be human readable for easier debugging.