pg: avoid hang on orphaned transcation panic (#1123)

When a test or an application panics due to an orphaned transaction
when trying to close the DB.  This change avoids the hang by
automatically rolling back the orphaned transaction and closing the DB
before the explicit panic.

node/pg/db.go

@@ -266,6 +266,16 @@ func (db *DB) EnsureFullReplicaIdentityDatasets(ctx context.Context) error {
 func (db *DB) Close() error {
 	db.cancel(nil)
 	db.repl.stop()
+	if db.tx != nil {
+		// This is a bug, so we are going to panic so the issue is not easily
+		// ignored, but we will rollback the tx so we don't hang or leak
+		// postgresql resources.
+		db.tx.Rollback(context.Background())
+		db.tx = nil
+		db.txid = ""
+		db.pool.Close()
+		panic("Closed the DB with an active transaction!")
+	}
 	return db.pool.Close()
 }