DESCRIBE EXTENDED date format should be non-ambiguous

[rmoff]

Currently DESCRIBE EXTENDED uses an ambiguous date format for last-message:

Local runtime statistics
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messages-per-sec:     50.30   total-messages:      5012     last-message: 10/5/18 9:54:06 AM UTC

Is this 10th May, or 5th October?!

I suggest we use a standard like https://en.wikipedia.org/wiki/ISO_8601 so:

2018-10-05T10:15:23+00:00

or at the very minimum, 2018-10-05 for the date portion of the timestamp