Exit if booted into a container image

This is part of coreos/fedora-coreos-tracker#1263

We don't yet have an official stance on how zincati and custom
container images interact.  Today, zincati just crash loops.
This changes things so that we gracefully exit if we detect
the booted system is using a container image origin.

(The code here isn't quite as clean as it could be; calling
 `std::process::exit()` in the middle of the call chain isn't
  elegant but doing better would require plumbing through an
  `Option<T>` through many layers)

src/identity/mod.rs

@@ -96,6 +96,17 @@ impl Identity {
         let basearch = coreos_stream_metadata::this_architecture().to_string();
         let current_os =
             rpm_ostree::parse_booted(&status).context("failed to introspect booted OS image")?;
+        let current_os = if let Some(o) = current_os {
+            o
+        } else {
+            log::info!("Disabling zincati automatic updates");
+            crate::utils::update_unit_status(
+                "Booted into container image; zincati updates disabled",
+            );
+            crate::utils::notify_ready();
+            crate::utils::notify_stopping();
+            std::process::exit(0);
+        };
         let node_uuid = {
             let app_id = id128::Id128::try_from_slice(APP_ID)
                 .map_err(|e| anyhow!("failed to parse application ID: {}", e))?;

src/rpm_ostree/cli_status.rs

@@ -48,6 +48,7 @@ pub struct StatusJson {
 #[serde(rename_all = "kebab-case")]
 pub struct DeploymentJson {
     booted: bool,
+    container_image_reference: Option<String>,
     base_checksum: Option<String>,
     #[serde(rename = "base-commit-meta")]
     base_metadata: BaseCommitMetaJson,
@@ -62,7 +63,7 @@ pub struct DeploymentJson {
 #[derive(Clone, Debug, Deserialize)]
 struct BaseCommitMetaJson {
     #[serde(rename = "fedora-coreos.stream")]
-    stream: String,
+    stream: Option<String>,
 }
 
 impl DeploymentJson {
@@ -84,13 +85,21 @@ impl DeploymentJson {
 }
 
 /// Parse the booted deployment from status object.
-pub fn parse_booted(status: &StatusJson) -> Result<Release> {
-    let json = booted_json(status)?;
-    Ok(json.into_release())
+pub fn parse_booted(status: &StatusJson) -> Result<Option<Release>> {
+    let status = booted_json(status)?;
+    if let Some(img) = status.container_image_reference.as_ref() {
+        log::info!("Booted system is tracking {img}");
+        return Ok(None);
+    }
+    Ok(Some(status.into_release()))
 }
 
 fn fedora_coreos_stream_from_deployment(deploy: &DeploymentJson) -> Result<String> {
-    let stream = deploy.base_metadata.stream.as_str();
+    let stream = deploy
+        .base_metadata
+        .stream
+        .as_ref()
+        .ok_or_else(|| anyhow!("Missing `fedora-coreos.stream` in commit metadata"))?;
     ensure!(!stream.is_empty(), "empty stream value");
     Ok(stream.to_string())
 }