daemon: Fix many errors (OER rather than OE)

daemon: Fix many errors (OER rather than OE)

Firstly, all these functions shuuld throw OER which is the thing which
implements the Rocket Responder trait, so that the error actually goes
back to the client.

Secondly, they all need ?.  Without that, these functions all always
succeed and always return Result::Ok(some Result<, OE[R]>).
Surprisingly this is accepted, because Result<> impl Responder
and apparently Result<Result<..>> does too!

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>