Implement SR.{attach,detach,create} where device_config contains a single "path"
Implement SR.{attach,detach,create} where device_config contains a single "path"

The "path" will be to a directory, which may or may not exist, which will
contain the virtual disk images and per-disk metadata.

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@eu.citrix.com>

xapi-project/ffs,robertbreker/ffs,djs55/ffs,franciozzy/ffs