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/mock_high_priority_service.hpp

@@ -23,6 +23,8 @@
 #include "wsrep/high_priority_service.hpp"
 #include "mock_client_state.hpp"
 
+#include <memory>
+
 namespace wsrep
 {
     class mock_high_priority_service : public wsrep::high_priority_service
@@ -38,8 +40,11 @@ namespace wsrep
             , fail_next_toi_()
             , client_state_(client_state)
             , replaying_(replaying)
+            , nbo_cs_()
         { }
 
+        ~mock_high_priority_service()
+        { }
         int start_transaction(const wsrep::ws_handle&, const wsrep::ws_meta&)
             WSREP_OVERRIDE;
 
@@ -65,6 +70,8 @@ namespace wsrep
         int apply_toi(const wsrep::ws_meta&,
                       const wsrep::const_buffer&,
                       wsrep::mutable_buffer&) WSREP_OVERRIDE;
+        int apply_nbo_begin(const wsrep::ws_meta&,
+                            const wsrep::const_buffer&) WSREP_OVERRIDE;
         void adopt_apply_error(wsrep::mutable_buffer& err) WSREP_OVERRIDE;
         void after_apply() WSREP_OVERRIDE;
         void store_globals() WSREP_OVERRIDE { }
@@ -84,11 +91,19 @@ namespace wsrep
         bool do_2pc_;
         bool fail_next_applying_;
         bool fail_next_toi_;
+
+        wsrep::mock_client* nbo_cs() const { return nbo_cs_.get(); }
+
     private:
         mock_high_priority_service(const mock_high_priority_service&);
         mock_high_priority_service& operator=(const mock_high_priority_service&);
         wsrep::mock_client_state* client_state_;
         bool replaying_;
+
+        /* Client state associated to NBO processing. This should be
+         * stored elsewhere (like mock_server_state), but is kept
+         * here for convenience. */
+        std::unique_ptr<wsrep::mock_client> nbo_cs_;
     };
 }