This fixes a bug where 'Worker undefined changed status' was logged in
the web interface, as that was (back then incorrectly) `workerupdate.name`.
Now that code is correct.
`persistence.Model` contains the common database fields for most model
structs. It is a copy of `gorm.Model`, but without the `DeletedAt`
field (which triggers Gorm's soft deletion).
Soft deletion is not used by Flamenco. If it ever becomes necessary to
support soft-deletion, see https://gorm.io/docs/delete.html#Soft-Delete
The canary test asserts that certain constants still have the expected
value. Lowering those constants is good for testing the timeout stuff with
the actual Flamenco Manager + Worker (without having to wait 5 minutes for
it to kick in), but it's too easy to accidentally run the unit tests and
get cryptic errors about everything failing horribly and miserably when
you leave those constants low.
