Use async account fetch instead of sync

This allows TestRPC to run in the same node process as the loopback app

index.js

@@ -5,5 +5,7 @@ var Web3 = require('./lib/web3');
 exports.initialize = function(dataSource, cb) {
   var settings = dataSource.settings;
   var connector = new Web3(settings);
+  connector.connect(cb);
+
   dataSource.connector = connector;
 };

lib/web3.js

@@ -13,18 +13,24 @@ function Web3Connector(settings) {
   this.settings = settings;
 
   const url = settings.url || 'http://localhost:8545';
-  const web3 = new Web3(new Web3.providers.HttpProvider(url));
-
-  if (web3.eth.accounts[0]) {
-    web3.eth.defaultAccount = web3.eth.accounts[0];
-  } else {
-    throw "error : can not connect to rpc server - please check datasources.json"
-  }
-  this.web3 = web3;
+  this.web3 = new Web3(new Web3.providers.HttpProvider(url));
 }
 
 Web3Connector.prototype.DataAccessObject = Web3DAO;
 
+Web3Connector.prototype.connect = function(cb) {
+  const web3 = this.web3;
+
+  web3.eth.getAccounts(function(err, accounts) {
+    if (err) {
+      return cb(err);
+    }
+
+    web3.eth.defaultAccount = accounts[0];
+    cb();
+  });
+}
+
 Web3Connector.prototype.define = function(modelData) {
   var web3 = this.web3;
   var model = modelData.model;