internal API for fetching MgsUpdateDriver status does not work

[davepacheco]

While debugging #8466, I tried to fetch the status from the MgsUpdateDriver, but it returned a 500 error. The Nexus log showed:

00:12:13.903Z INFO bea4cc1e-0758-4643-a4b4-669f67689c6c (dropshot_internal): request completed
    error_message_external = Internal Server Error
    error_message_internal = key must be a string
    file = /home/build/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/dropshot-0.16.2/src/server.rs:855
    latency_us = 6461
    local_addr = [fd00:1122:3344:102::4]:12221
    method = GET
    remote_addr = [fd00:1122:3344:103::2]:47733
    req_id = 3c6fc474-7d95-4eb1-ae18-da944fb176ff
    response_code = 500
    uri = /mgs-updates

This is a serde serialization error being reported when dropshot tries to serialize the return value. The problem is that this structures has a BTreeMap whose key is a BaseboardId, which does not itself serialize to a string. Elsewhere when we needed this, we switched to an IdMap anyway. That serializes to an array of objects, which avoids this problem. Here, I've switched it to an iddqd::IdOrdMap.

This PR currently has two commits:

• The first one adds a test that shows that the serialization of MgsUpdateDriverStatus doesn't work.
• The second one fixes it by fixing the structure to use an IdOrdMap instead.

[sunshowers]

looks good, thanks!

[sunshowers]

add expect here?

[sunshowers]

Can just be &'a BaseboardId I think

[sunshowers]

(I think the Arc was added to allow cheap cloning for keys in IdMaps. Since iddqd can work with borrowed forms, it shouldn't really be necessary
to have Arc at all once all users have moved over)

[davepacheco]

I'm not positive but I don't think so. I'm assuming that would make these structs borrow from somewhere else, but they get sent over a watch channel so I'm not sure how that would work. Also, I think the source of these is MgsUpdateDriver, which also keeps these as Arc, and shares them with the inventory collection that they originally were found in.

[sunshowers]

Hmm, that wouldn't stop this specific spot from being &'a BaseboardId I think?

[davepacheco]

I see now -- done in #8477.

[davepacheco]

Thanks for the review!