copy: change the various copy_xyz() calls to take a unified flags parameter

This adds a unified "copy_flags" parameter to all copy_xyz() function
calls, replacing the various boolean flags so far used. This should make
many invocations more readable as it is clear what behaviour is
precisely requested. This also prepares ground for adding support for
more modes later on.

src/shared/machine-image.c

@@ -594,7 +594,7 @@ static int clone_auxiliary_file(const char *path, const char *new_name, const ch
         if (!rs)
                 return -ENOMEM;
 
-        return copy_file_atomic(path, rs, 0664, false, 0);
+        return copy_file_atomic(path, rs, 0664, 0, COPY_REFLINK);
 }
 
 int image_clone(Image *i, const char *new_name, bool read_only) {
@@ -656,7 +656,7 @@ int image_clone(Image *i, const char *new_name, bool read_only) {
         case IMAGE_RAW:
                 new_path = strjoina("/var/lib/machines/", new_name, ".raw");
 
-                r = copy_file_atomic(i->path, new_path, read_only ? 0444 : 0644, false, FS_NOCOW_FL);
+                r = copy_file_atomic(i->path, new_path, read_only ? 0444 : 0644, FS_NOCOW_FL, COPY_REFLINK);
                 break;
 
         default: