libvirt.test: Add more options test for attach-disk

Add some more test for attach-disk, for example:
--serial, --address, --multifunction, --subdriver, etc.

Signed-off-by: Li Yang <liyang.fnst@cn.fujitsu.com>
@liyangfnst , Hi. The interchange using of `Tab` and space in this line is causing error when using `--list-tests` option. could please help check this out?
```
# ./run -t libvirt --list-tests 
Internal error, traceback follows...
Traceback (most recent call last):
  File "./run", line 904, in _process_options
    self.cartesian_parser.parse_file(cfg)
  File "/tmp/virt-test-smoke-222/virttest/cartesian_config.py", line 1341, in parse_file
    self.node = self._parse(Lexer(FileReader(filename)), self.node)
  File "/tmp/virt-test-smoke-222/virttest/cartesian_config.py", line 1715, in _parse
    node = self._parse(lch, node, -1)
  File "/tmp/virt-test-smoke-222/virttest/cartesian_config.py", line 1715, in _parse
    node = self._parse(lch, node, -1)
  File "/tmp/virt-test-smoke-222/virttest/cartesian_config.py", line 1562, in _parse
    node3 = self._parse(lexer, node2, prev_indent=indent)
  File "/tmp/virt-test-smoke-222/virttest/cartesian_config.py", line 1562, in _parse
    node3 = self._parse(lexer, node2, prev_indent=indent)
  File "/tmp/virt-test-smoke-222/virttest/cartesian_config.py", line 1562, in _parse
    node3 = self._parse(lexer, node2, prev_indent=indent)
  File "/tmp/virt-test-smoke-222/virttest/cartesian_config.py", line 1517, in _parse
    lexer.get_next_check_nw([LVariant])
  File "/tmp/virt-test-smoke-222/virttest/cartesian_config.py", line 1193, in get_next_check_nw
    self.line, self.filename, self.linenum)
ParserError: Expected ['-'] got ['only']: 'only attach_disk' (/tmp/virt-test-smoke-222/backends/libvirt/cfg/subtests.cfg:7463)
```