Since the change "block_tester: limit batching in sequential test", the
sequence test blocks infinitely when encountering a length value smaller
than the block size.
- Added 'io_buffer' attribute, default is 4M
- Added 'batch' attribute, specifying the number of jobs used
in parallel, default is 1 (sequential)
- Removed 'synchronous' attribute (use batch of 1 instead)
- Added 'copy' attribute (default "yes")
- Print number of signals ("triggered")
Issue #3283
