Use hostname for Baseboard::Pc::identifier field (#4937)

Doing this allows easier testbed setup and usage since we identify new
sleds to add via their baseboard. In case we can't get a hostname we
revert to using a UUID, as in the prior version of code.

Cargo.toml

@@ -208,6 +208,7 @@ gateway-client = { path = "clients/gateway-client" }
 gateway-messages = { git = "https://github.com/oxidecomputer/management-gateway-service", rev = "2739c18e80697aa6bc235c935176d14b4d757ee9", default-features = false, features = ["std"] }
 gateway-sp-comms = { git = "https://github.com/oxidecomputer/management-gateway-service", rev = "2739c18e80697aa6bc235c935176d14b4d757ee9" }
 gateway-test-utils = { path = "gateway-test-utils" }
+gethostname = "0.4.3"
 glob = "0.3.1"
 guppy = "0.17.4"
 headers = "0.3.9"

sled-hardware/Cargo.toml

@@ -10,6 +10,7 @@ anyhow.workspace = true
 camino.workspace = true
 cfg-if.workspace = true
 futures.workspace = true
+gethostname.workspace = true
 illumos-utils.workspace = true
 libc.workspace = true
 macaddr.workspace = true

sled-hardware/src/illumos/mod.rs

@@ -7,6 +7,7 @@ use crate::{
     UnparsedDisk,
 };
 use camino::Utf8PathBuf;
+use gethostname::gethostname;
 use illumos_devinfo::{DevInfo, DevLinkType, DevLinks, Node, Property};
 use omicron_common::disk::DiskIdentity;
 use slog::debug;
@@ -525,7 +526,9 @@ fn poll_device_tree(
 
                         if inner.baseboard.is_none() {
                             let pc_baseboard = Baseboard::new_pc(
-                                Uuid::new_v4().simple().to_string(),
+                                gethostname().into_string().unwrap_or_else(
+                                    |_| Uuid::new_v4().simple().to_string(),
+                                ),
                                 root_node.clone(),
                             );