Fix lcli testnet deployer

lcli/Cargo.toml

@@ -23,3 +23,4 @@ futures = "0.1.25"
 environment = { path = "../lighthouse/environment" }
 web3 = "0.8.0"
 eth2_testnet = { path = "../eth2/utils/eth2_testnet" }
+dirs = "2.0"

lcli/src/main.rs

@@ -159,8 +159,7 @@ fn main() {
                         .short("o")
                         .value_name("PATH")
                         .takes_value(true)
-                        .default_value("~/.lighthouse/testnet")
-                        .help("The output directory."),
+                        .help("The output directory. Defaults to ~/.lighthouse/testnet"),
                 )
                 .arg(
                     Arg::with_name("min_genesis_time")

lcli/src/testnet.rs

@@ -6,6 +6,8 @@ use std::path::PathBuf;
 use types::EthSpec;
 use web3::{transports::Http, Web3};
 
+pub const DEFAULT_DATA_DIR: &str = ".lighthouse/testnet";
+
 pub fn new_testnet<T: EthSpec>(
     mut env: Environment<T>,
     matches: &ArgMatches,
@@ -24,9 +26,16 @@ pub fn new_testnet<T: EthSpec>(
 
     let output_dir = matches
         .value_of("output")
-        .ok_or_else(|| "Output directory not specified")?
-        .parse::<PathBuf>()
-        .map_err(|e| format!("Failed to parse output directory: {}", e))?;
+        .ok_or_else(|| ())
+        .and_then(|output| output.parse::<PathBuf>().map_err(|_| ()))
+        .unwrap_or_else(|_| {
+            dirs::home_dir()
+                .map(|mut home| {
+                    home.push(DEFAULT_DATA_DIR);
+                    home
+                })
+                .expect("should locate home directory")
+        });
 
     let endpoint = matches
         .value_of("endpoint")
@@ -73,6 +82,8 @@ pub fn new_testnet<T: EthSpec>(
         deploy_block
     );
 
+    info!("Writing config to {:?}", output_dir);
+
     Eth2TestnetDir::new(
         output_dir,
         format!("0x{}", deposit_contract.address()),