needs a way to get precise timings on pqm landings

[Vincent Ladeuil]

We lack a way to get precise timings from pqm. This makes diagnosing issues on pqm hard.

We can get the logs from there (there is a cronjob mirroring them on chinstrap) but they are almost empty (they contain some error messages when the landing fail) and gives only an end date (when rsync'ed).

Adding some messages with `date` to the log files sounds like a simple first step.

[Robert Collins (lifeless)]

You could make pqm itself capture more or log things differently, as
an alternative approach. (And the subunit logs are totally datestamped
too)