pkg/updateengine: Return the right error on Call failures

[dghubble]

On call errors, the err from the Hello was returned instead of the call.Err reason for the call failure.

[sdemos]

lgtm. +1 on removing the named returns.

[sdemos]

actually, is there any reason why you didn't also remove the named returns on the New function? it looks like they are defined there but the behavior is ignored and everything is just directly returning instead.

[dghubble]

Yeah, we could drop the named returns.

c := new(Client)
var err error