add a hook for plugins to perform asyncronous initialization.

needed for SFE to enable deployment profiles

lib/Serverless.js

@@ -70,7 +70,8 @@ class Serverless {
     }).then(() => {
       // load all plugins
       this.pluginManager.loadAllPlugins(this.service.plugins);
-
+      return this.pluginManager.asyncPluginInit();
+    }).then(() => {
       // give the CLI the plugins and commands so that it can print out
       // information such as options when the user enters --help
       this.cli.setLoadedPlugins(this.pluginManager.getPlugins());

lib/classes/PluginManager.js

@@ -549,6 +549,10 @@ class PluginManager {
       }
     });
   }
+
+  asyncPluginInit() {
+    return BbPromise.map(this.plugins, plugin => (plugin.asyncInit && plugin.asyncInit()));
+  }
 }
 
 module.exports = PluginManager;