cmd: show useful error when tm not initialised (#4512)

Closes #4303

Before:

```
TMHOME="/Users/daniel/go/src/github.com/tendermint/thome" tendermint node --proxy_app=unix:///Users/daniel/go/src/github.com/kvstore/example.sock

ERROR: 1 error(s) decoding:

* error decoding 'consensus.create_empty_blocks_interval': time: invalid duration
```

After:

```
$ TMHOME=/tmp ./build/tendermint node --proxy_app=kvstore
ERROR: failed to create node: Couldn't read GenesisDoc file: open /tmp/config/genesis.json: no such file or directory
```

cmd/tendermint/commands/run_node.go

@@ -78,7 +78,7 @@ func AddNodeFlags(cmd *cobra.Command) {
 		"Set this to false to only produce blocks when there are txs or when the AppHash changes")
 	cmd.Flags().String(
 		"consensus.create_empty_blocks_interval",
-		string(config.Consensus.CreateEmptyBlocksInterval),
+		config.Consensus.CreateEmptyBlocksInterval.String(),
 		"The possible interval between empty blocks")
 
 	// db flags
@@ -99,11 +99,21 @@ func NewRunNodeCmd(nodeProvider nm.Provider) *cobra.Command {
 		Use:   "node",
 		Short: "Run the tendermint node",
 		RunE: func(cmd *cobra.Command, args []string) error {
+			if err := checkGenesisHash(config); err != nil {
+				return err
+			}
+
 			n, err := nodeProvider(config, logger)
 			if err != nil {
-				return fmt.Errorf("failed to create node: %v", err)
+				return fmt.Errorf("failed to create node: %w", err)
 			}
 
+			if err := n.Start(); err != nil {
+				return fmt.Errorf("failed to start node: %w", err)
+			}
+
+			logger.Info("Started node", "nodeInfo", n.Switch().NodeInfo())
+
 			// Stop upon receiving SIGTERM or CTRL-C.
 			tmos.TrapSignal(logger, func() {
 				if n.IsRunning() {
@@ -111,15 +121,6 @@ func NewRunNodeCmd(nodeProvider nm.Provider) *cobra.Command {
 				}
 			})
 
-			if err := checkGenesisHash(config); err != nil {
-				return err
-			}
-
-			if err := n.Start(); err != nil {
-				return fmt.Errorf("failed to start node: %v", err)
-			}
-			logger.Info("Started node", "nodeInfo", n.Switch().NodeInfo())
-
 			// Run forever.
 			select {}
 		},