guestfish_block_dev: Add 3 scrub related cases

1.scrub-device
2.scrub-device
3.scrub-freespace
guestfish_block_dev: Add md device related case

1. md-create
2. md-detail
3. md-stop
4. md-stat
5. list-md-devices
guestfish_block_dev: Add part_add, part_del, part_init cases
guestfish_block_dev: Add cases to test API

part-set-bootable
part-get-bootable
part-set-mbr-id
part-get-mbr-id
Merge pull request #126 from vanbogithub/bfan-dev

Add some scrub and md device related cases