use --dev when in development

lib/cmds/blockchain/blockchain.js

@@ -55,7 +55,12 @@ var Blockchain = function(options) {
 
 Blockchain.prototype.runCommand = function(cmd, options) {
   console.log(("running: " + cmd.underline).green);
-  return shelljs.exec(cmd, options);
+  return shelljs.exec(cmd, options, (err, stdout, _stderr) => {
+    if (err && this.env === 'development' && stdout.indexOf('Failed to unlock developer account') > 0) {
+      console.warn('\nDevelopment blockchain changed to use the --dev option.'.yellow);
+      console.warn('You will need to change your data directory in blockchain.json (datadir)'.yellow);
+    }
+  });
 };
 
 Blockchain.prototype.run = function() {
@@ -69,7 +74,10 @@ Blockchain.prototype.run = function() {
     console.log(("could not find " + this.config.geth_bin + " command; is " + this.client.name + " installed or in the PATH?").green);
     return;
   }
-  var address = this.initChainAndGetAddress();
+  let address = '';
+  if (self.env !== "development") {
+    address = this.initChainAndGetAddress();
+  }
   this.client.mainCommand(address, function(cmd) {
     self.runCommand(cmd, {async: true});
   });

lib/cmds/blockchain/geth_commands.js

@@ -123,6 +123,7 @@ class GethCommands {
     let config = this.config;
     let rpc_api = (this.config.rpcApi || ['eth', 'web3', 'net']);
     let ws_api = (this.config.wsApi || ['eth', 'web3', 'net']);
+    const isDev = self.env === 'development';
 
     async.series([
       function commonOptions(callback) {
@@ -188,7 +189,7 @@ class GethCommands {
         } else {
           accountAddress = address;
         }
-        if (accountAddress) {
+        if (accountAddress && !isDev) {
           return callback(null, "--unlock=" + accountAddress);
         }
         callback(null, "");
@@ -200,10 +201,16 @@ class GethCommands {
         callback(null, "");
       },
       function mineWhenNeeded(callback) {
-        if (config.mineWhenNeeded) {
+        if (config.mineWhenNeeded && !isDev) {
           return callback(null, "js .embark/" + self.env + "/js/mine.js");
         }
         callback(null, "");
+      },
+      function isDev(callback) {
+        if (isDev) {
+          return callback(null, '--dev');
+        }
+        callback(null, '');
       }
     ], function (err, results) {
       if (err) {