Move plugin init to the end of main()
Move plugin init to the end of main()

It sometimes occurs that the plugin initialization will fail
because the plugin preprocessor is not created yet.

SkygearIO/skygear-server,rickmak/skygear-server,rickmak/skygear-server,rickmak/skygear-server,SkygearIO/skygear-server,SkygearIO/skygear-server,SkygearIO/skygear-server