[unpackfs] Skip overlay extended attributes

The module preserves the extended attributes at rsync and the overlay
filesystem stores extended attributes by inodes.

The overlay filesystem keeps traces of the lower directory by encoding
and storing its UUID to the attribute trusted.overlay.origin. If the
index feature is on, that attribute is compared to the UUID of the lower
directory at every subsequent mounts and causes mount to fail with
ESTATE if it does not match.

This filters the namespace trusted.overlay.* by using the rsync option
--filter='-x trusted.overlay.*' to make sure the overlays extended
attributes are not preserved.

Fixes:
        # mount -t overlay -o lowerdir=...,upperdir,...,workdir= overlay /mnt/etc
        mount: /var/mnt/etc: mount(2) system call failed: Stale file handle.

        # dmesg
        (...)
        overlayfs: "xino" feature enabled using 32 upper inode bits.
        overlayfs: failed to verify origin (/etc, ino=524292, err=-116)
        overlayfs: failed to verify upper root origin

src/modules/unpackfs/main.py

@@ -181,7 +181,7 @@ def file_copy(source, entry, progress_cb):
     num_files_total_local = 0
     num_files_copied = 0  # Gets updated through rsync output
 
-    args = ['rsync', '-aHAXr']
+    args = ['rsync', '-aHAXr', '--filter=-x trusted.overlay.*']
     args.extend(global_excludes())
     if entry.excludeFile:
         args.extend(["--exclude-from=" + entry.excludeFile])