cmd, core, eth, common: genesis preparation

Implemented the --genesis flag thru which we can set a custom genesis
block, including the official Ethereum genesis block.

tests/block_test_util.go

@@ -160,6 +160,8 @@ func runBlockTests(bt map[string]*BlockTest, skipTests []string) error {
 }
 func runBlockTest(test *BlockTest) error {
 	cfg := test.makeEthConfig()
+	cfg.GenesisBlock = test.Genesis
+
 	ethereum, err := eth.New(cfg)
 	if err != nil {
 		return err
@@ -170,9 +172,6 @@ func runBlockTest(test *BlockTest) error {
 		return err
 	}
 
-	// import the genesis block
-	ethereum.ResetWithGenesisBlock(test.Genesis)
-
 	// import pre accounts
 	statedb, err := test.InsertPreState(ethereum)
 	if err != nil {