s390x: remove 'sdboot' before generating new one

Since s390-tools commit f4cf4ae6ebb1 ("rust: Add a new tool called 'pvimg'") the
C 'genprotimg' tool no longer exists and was replaced by symlink to Rust 'pvimg create',
which by default doens't overwrite the output image.
For backward compatibility let's silently remove the 'sdboot'.

Author: nikita-dubrovskii

docs/release-notes.md

@@ -13,7 +13,7 @@ Minor changes:
 
 
 Internal changes:
-
+- s390x: remove 'sdboot' before generating new one
 
 Packaging changes:
 

src/s390x/zipl.rs

@@ -281,6 +281,13 @@ fn generate_sdboot(
 
     // finally, Secure Execution sd-boot image
     let sdboot = mountpoint.join("sdboot");
+
+    // C 'genprotimg' tool no longer exists and was replaced by symlink to Rust 'pvimg create',
+    // which by default doens't overwrite the output image.
+    // For backward compatibility let's silently remove the 'sdboot'.
+    let _ = std::fs::remove_file(&sdboot);
+
+    // FIXME: in F42/el10 switch to 'pvimg create' with '--overwrite' flag.
     let mut cmd = Command::new("genprotimg");
     cmd.arg("--verbose")
         .arg("--image")