CA-122205: Continuation to the previous commits

Tests have uncovered additional failures, expanding error handler
to catch ENOENT againt OSError and EIO against CommandException

Signed-off-by: Vineeth Thampi Raveendran <vineeth.thampi@citrix.com>
Reviewed-by: Thanos Makatos <thanos.makatos@citrix.com>

GitHub: closes #94 on xapi-project/sm