`omdb nexus update-status` shows status for sleds that aren't part of the cluster

[jgallagher]

During today's dogfood update, we noticed this in omdb nexus status (trimming out unrelated, expected lines):

Installed RoT Bootloader Software
BASEBOARD_ID            STAGE0_VERSION             STAGE0_NEXT_VERSION
913-0000019:BRM42220018 17.0.0-0.ci+git76ec1fa523c 17.0.0-0.ci+git76ec1fa523c

Installed RoT Software
BASEBOARD_ID            SLOT_A_VERSION                      SLOT_B_VERSION
913-0000019:BRM42220018 17.0.0-0.ci+git76ec1fa523c          17.0.0-0.ci+git76ec1fa523c (active)

Installed SP Software
BASEBOARD_ID            SLOT0_VERSION              SLOT1_VERSION
913-0000019:BRM42220018 17.0.0-0.ci+git76ec1fa523c 17.0.0-0.ci+git76ec1fa523c

Installed Host Phase 1 Software
BASEBOARD_ID            SLED_ID                              SLOT_A_VERSION   SLOT_B_VERSION
913-0000019:BRM42220018                                      unknown (active) unknown

Sled BRM42220018 is not part of the control plane cluster, and we shouldn't be reporting update status for it. It is physically present, so we collect information from it as part of inventory, which is presumably why we're seeing it here.

(We don't yet have the external update status API on this commit, so I'm not sure if it's also affected - I would naively assume it is since we used the internal update status as a starting point. CC @david-crespo)