Extend ethclient test, implement new TxID spec

- Implement new TxID spec that distinguishes L1UserTx and L1CoordinatorTx
- Replace some type []*Foo by []Foo
- Fix HistoryDB & L2DB bug: in case of error, a rollback was applied and the returned error was nil
- Reorder inserts in historydb.NewHistoryDB() to follow foreign key dependencies
- Add initial synchronizer test with test.Client (for now, only tested l1UserTxs, blocks, addToken)
- Update L1UserTx event in test.Client

db/l2db/l2db.go

@@ -7,6 +7,7 @@ import (
 
 	ethCommon "github.com/ethereum/go-ethereum/common"
 	"github.com/hermeznetwork/hermez-node/common"
+	"github.com/hermeznetwork/hermez-node/log"
 	"github.com/iden3/go-iden3-crypto/babyjub"
 	"github.com/jmoiron/sqlx"
 
@@ -212,7 +213,10 @@ func (l2db *L2DB) CheckNonces(updatedAccounts []common.Account, batchNum common.
 	defer func() {
 		// Rollback the transaction if there was an error.
 		if err != nil {
-			err = txn.Rollback()
+			errRollback := txn.Rollback()
+			if errRollback != nil {
+				log.Errorw("Rollback", "err", errRollback)
+			}
 		}
 	}()
 	for i := 0; i < len(updatedAccounts); i++ {
@@ -257,7 +261,10 @@ func (l2db *L2DB) Purge(currentBatchNum common.BatchNum) (err error) {
 	defer func() {
 		// Rollback the transaction if there was an error.
 		if err != nil {
-			err = txn.Rollback()
+			errRollback := txn.Rollback()
+			if errRollback != nil {
+				log.Errorw("Rollback", "err", errRollback)
+			}
 		}
 	}()
 	// Delete pending txs that have been in the pool after the TTL if maxTxs is reached