Clean up rustfmt check_closed_event expansion in shutdown_tests

`rustfmt` loves to make expressions vertical by putting each method
parameter on its own line. In cases where each method parameter is
actually doing something, this can be fine, but in some cases we
have a few method parameters that are straightforward and shouldn't
be the readers focus, mixed with one or two parameters which are
key.

Here, we clean up a regular instance of this in calls to
`check_closed_event` in `shutdown_tests.rs`. It breaks out the
`ClosureReason` (the thing that usually is being tested for) from
the remaining parameters, which are fairly straightforward and not
the important points, leaving the rest of `check_closed_event` on
one line.

This also fixes some instances where `rustfmt` refused to format
code entirely.

Author: TheBlueMatt