private/dbutil: rollback pending transactions on panic

We don't do a lot of panicking in our main code, so hopefully this won't
matter much, but we /do/ call panic a lot in our tests (t.Fatal,
require.NoError, etc). And when that happens, we need pending
transactions to be aborted or we can get into a deadlock situation when
something else tries to /Close/ that connection.

Change-Id: Idaf0d543ac95afea34f9b2393d1187f5322e9f0f

private/dbutil/txutil/transactions.go

@@ -36,6 +36,11 @@ func ExecuteInTx(ctx context.Context, dbDriver driver.Driver, tx txLike, fn func
 		return crdb.ExecuteInTx(ctx, tx, fn)
 	}
 	defer func() {
+		if x := recover(); x != nil {
+			// does nothing if tx is already rolled back or committed.
+			_ = tx.Rollback()
+			panic(x)
+		}
 		if err == nil {
 			err = tx.Commit()
 		} else {