Support vdi_revert on FileSR

* Support vdi_revert from xapi
* Enable VDI_REVERT capability on FileSR
* Implement vdi revert on FileSR
* Support vdi_revert rollback with journal in case of catastrophic failure
* Fix ZFSSR tests

Signed-off-by: Antoine Bartuccio <antoine.bartuccio@vates.tech>

Author: klmp200