Lookup user by id, not username - fixes AR::RecordNotFound [WIP-334]

Fixes: https://assembly.com/coderwall/wips/334

RefreshUserJob performs a lookup by user_id rather than username.  `line 8: user = User.find(user_id)`

Errors in production were averaging 6% and spiking to 12%.  This should fix a majority of those errors.