client session ssh BUGFIX flush after print without newline

Fixes cesnet/netopeer2#769
diff --git a/src/session_client_ssh.c b/src/session_client_ssh.c
index 0710d21..7097e8e 100644
--- a/src/session_client_ssh.c
+++ b/src/session_client_ssh.c
@@ -437,6 +437,7 @@
                     ERR("Writing into output failed (%s).", feof(out) ? "EOF" : strerror(errno));
                     goto error;
                 }
+                fflush(out);
             }
         } while (strcmp(answer, "yes") && strcmp(answer, "no"));