Added test for FUA acceptance.

Although I think this might be a bit useless as servers normally just
ingore flags.

src/server/client.c

@@ -483,6 +483,7 @@ void client_reply_to_write( struct client* client, struct nbd_request request )
 		/* multiple of 4K page size */
 		uint64_t from_rounded = request.from & (!0xfff);
 		uint64_t len_rounded = request.len + (request.from - from_rounded);
+		debug("Calling msync from=%"PRIu64", len=%"PRIu64"",from_rounded, len_rounded);
 
 		FATAL_IF_NEGATIVE(
 			msync( client->mapped + from_rounded,