Download snapshot files with a tmp- prefix so they'll automatically be cleaned up if interrupted

(cherry picked from commit 58b980f9cd)

download-utils/src/lib.rs

@@ -34,9 +34,18 @@ pub fn download_file(
     }
     let download_start = Instant::now();
 
-    fs::create_dir_all(destination_file.parent().unwrap()).map_err(|err| err.to_string())?;
+    fs::create_dir_all(destination_file.parent().expect("parent"))
+        .map_err(|err| err.to_string())?;
 
-    let temp_destination_file = destination_file.with_extension("tmp");
+    let mut temp_destination_file = destination_file.to_path_buf();
+    temp_destination_file.set_file_name(format!(
+        "tmp-{}",
+        destination_file
+            .file_name()
+            .expect("file_name")
+            .to_str()
+            .expect("to_str")
+    ));
 
     let progress_bar = new_spinner_progress_bar();
     if use_progress_bar {