Send on create confirmation email after commit (#4064)

Call send_on_create_confirmation_instructions in after_commit instead of after_create, I think this is no harm in general and it makes things like async job work.

Fix #4062

Gemfile

@@ -12,6 +12,7 @@ group :test do
   gem "omniauth-openid", "~> 1.0.1"
   gem "webrat", "0.7.3", require: false
   gem "mocha", "~> 1.1", require: false
+  gem 'test_after_commit', require: false
 end
 
 platforms :jruby do