Update reboot-required file with staged image context

This change updates the /run/reboot-required file to include information
about the staged bootc image digest. This will provide users with
information about what bootc image will be effective after the system
has been rebooted.

Fixes #1574
Signed-off-by: Brendan Shephard <bshephar@bne-home.net>

Author: bshephar

crates/lib/src/deploy.rs

@@ -794,9 +794,13 @@ pub(crate) async fn stage(
 
     // Unconditionally create or update /run/reboot-required to signal a reboot is needed.
     // This is monitored by kured (Kubernetes Reboot Daemon).
+    let reboot_message = format!(
+        "Reboot required for bootc image digest: {}",
+        image.manifest_digest.as_ref()
+    );
     let run_dir = Dir::open_ambient_dir("/run", cap_std::ambient_authority())?;
     run_dir
-        .atomic_write("reboot-required", b"")
+        .atomic_write("reboot-required", reboot_message.as_bytes())
         .context("Creating /run/reboot-required")?;
 
     Ok(())

tmt/tests/booted/test-image-pushpull-upgrade.nu

@@ -65,9 +65,9 @@ RUN echo test content > /usr/share/blah.txt
     let progress = open --raw $progress_json | from json -o
     sanity_check_switch_progress_json $progress
 
-    # Check that /run/reboot-required exists and is a zero-byte file
+    # Check that /run/reboot-required exists and is not empty
     let rr_meta = (ls /run/reboot-required | first)
-    assert equal $rr_meta.size 0b
+    assert ($rr_meta.size > 0b)
 
     # Also test that the mtime changes on modification
     let new_root_mtime = ls -Dl /ostree/bootc | get modified