TESTS: Change all tests to use 'block_size' instead of hardcoded 512

This should allow the testst to work corectly on block devices with 4k blocksize too.

test-tool/0193_writesame16_wrprotect.c

@@ -27,7 +27,7 @@ int T0193_writesame16_wrprotect(const char *initiator, const char *url, int data
 	struct scsi_readcapacity16 *rc16;
 	int ret, i, lun;
 	uint32_t block_size;
-	unsigned char buf[512];
+	unsigned char buf[4096];
 
 	printf("0193_writesame16_wrptotect:\n");
 	printf("=======================\n");