add logs at the end of unpacking (#4380)

We are currently logging progression when unpacking, but we're missing
the last log. This can be useful to monitor what's going on in CF.

Author: paulsemel

src/clusterfuzz/_internal/system/archive.py

@@ -181,6 +181,8 @@ def extract_all(self,
       if archive_file_unpack_count % 1000 == 0:
         logs.info('Unpacked %d/%d.' % (archive_file_unpack_count,
                                        archive_file_total_count))
+    logs.info('Unpacked %d/%d. Done.' % (archive_file_unpack_count,
+                                         archive_file_total_count))
 
     return not error_occurred