channeldb/test: test with postgres

kvdb/postgres/fixture_interface.go

@@ -0,0 +1,8 @@
+package postgres
+
+import "github.com/btcsuite/btcwallet/walletdb"
+
+type Fixture interface {
+	DB() walletdb.DB
+	Dump() (map[string]interface{}, error)
+}