routing: add option to force import MC pair history

This commit adds the `force` flag to the `XImportMissionControl` RPC
which allows skipping rules around the pair import except for what is
mandatory to make values meaningful. This can be useful for when clients
would like to forcibly override MC state in order to manipulate routing
results.

routing/missioncontrol.go

@@ -363,7 +363,9 @@ func (m *MissionControl) GetHistorySnapshot() *MissionControlSnapshot {
 // ImportHistory imports the set of mission control results provided to our
 // in-memory state. These results are not persisted, so will not survive
 // restarts.
-func (m *MissionControl) ImportHistory(history *MissionControlSnapshot) error {
+func (m *MissionControl) ImportHistory(history *MissionControlSnapshot,
+	force bool) error {
+
 	if history == nil {
 		return errors.New("cannot import nil history")
 	}
@@ -374,7 +376,7 @@ func (m *MissionControl) ImportHistory(history *MissionControlSnapshot) error {
 	log.Infof("Importing history snapshot with %v pairs to mission control",
 		len(history.Pairs))
 
-	imported := m.state.importSnapshot(history)
+	imported := m.state.importSnapshot(history, force)
 
 	log.Infof("Imported %v results to mission control", imported)
 
@@ -520,7 +522,7 @@ func (m *MissionControl) applyPaymentResult(
 		}
 
 		m.state.setLastPairResult(
-			pair.From, pair.To, result.timeReply, &pairResult,
+			pair.From, pair.To, result.timeReply, &pairResult, false,
 		)
 	}