NBO applying

- High priority interface method to apply NBO begin, separate from
  apply_toi() in order to avoid implementation to force interpreting
  ws_meta flags.
- Method to put client_state into NBO mode when applying NBO begin.
  The client_state will process in m_local mode.
- Unit tests for applying NBO

test/transaction_test.cpp

@@ -998,6 +998,8 @@ BOOST_FIXTURE_TEST_CASE(
 BOOST_FIXTURE_TEST_CASE(transaction_1pc_applying,
                         applying_client_fixture)
 {
+    start_transaction(wsrep::transaction_id(1),
+                      wsrep::seqno(1));
     BOOST_REQUIRE(cc.before_commit() == 0);
     BOOST_REQUIRE(tc.state() == wsrep::transaction::s_committing);
     BOOST_REQUIRE(cc.ordered_commit() == 0);