Libguestfs: Guestfs block oper

Testcases:
1.Get block information: block-getsz, block-getss, block-getbsz, block-getsize64
2.Set block size to half of current size: block-setbsz
3.Test readonly of block: block-getro, block-setro
4.Test r/w of block: block-setrw

Bug of testcase2:
Failed when I try to set a new blocksize.Block size without change after setting.