Review fixes

* Move resetting is_bf_immutable_ into trasaction::cleanup()
  to ensure that it is reset to false regardless how the
  transaction terminates.
* Removed redundant lock()/unlock() methods from
  mock_client_state.

src/transaction.cpp

@@ -648,7 +648,6 @@ int wsrep::transaction::after_commit()
  }
  assert(ret == 0);
  state(lock, s_committed);
- is_bf_immutable_ = false;
  debug_log_state("after_commit_leave");
  return ret;
 }
@@ -828,7 +827,6 @@ int wsrep::transaction::after_statement()
  state() == s_must_abort ||
  state() == s_cert_failed ||
  state() == s_must_replay);
- assert(not is_bf_immutable_);
 
  if (state() == s_executing &&
  streaming_context_.fragment_size() &&
@@ -2110,6 +2108,7 @@ void wsrep::transaction::cleanup()
  client_service_.cleanup_transaction();
  apply_error_buf_.clear();
  xid_.clear();
+ is_bf_immutable_ = false;
  debug_log_state("cleanup_leave");
 }
 

test/mock_client_state.hpp

@@ -49,8 +49,6 @@ namespace wsrep
  (void)client_service().bf_rollback();
  }
  }
- void lock() { mutex_.lock(); }
- void unlock() { mutex_.unlock(); }
  private:
  wsrep::default_mutex mutex_;
  wsrep::default_condition_variable cond_;