TESTS: Fix COMPAREANDWRITE tests to send write data

Previously COMPAREANDWRITE was only sending verify instance data which
can cause targets to generate COMMAND ABORTED/NOT ENOUGH UNSOLICITED
DATA errors due to the buffer being obviously too small to contain
verify AND write instance data.

The buffer size check has been modified and compareandwrite tests
updated to pass a larger buffer with interesting write instance data.

lib/iscsi-command.c

@@ -981,9 +981,9 @@ iscsi_compareandwrite_task(struct iscsi_context *iscsi, int lun, uint64_t lba,
 	struct scsi_task *task;
 	struct iscsi_data d;
 
-	if (datalen % blocksize != 0) {
+	if (datalen % (blocksize * 2) != 0) {
 		iscsi_set_error(iscsi, "Datalen:%d is not a multiple of the "
-				"blocksize:%d.", datalen, blocksize);
+				"blocksize * 2:%d.", datalen, blocksize * 2);
 		return NULL;
 	}