When test cannot be done with SCSI fallback to block layer

[baruch]

If we test a non-SCSI disk such as an SD card or a CF card, or just an old PATA drive it may not be handled through a SCSI layer or even a SCSI translation layer (as happens for SATA devices). In that case we need to detect it and fallback to a posix like scan with block layer read/write commands and ignore the low level protocol features.

[baruch]

Duplicates #36