Typo and update for ubuntu 16*

[slarue]

Hello,

1 - there is a little typo in the block to create backup user in mongodb

user: "backup”,
should be
user: "backup", (check the last " )

2 - for one who want to install this on Ubuntu 16*, there is a special process for mongoDb because ubuntu 16 use systemd instead of initd , for ex: https://www.digitalocean.com/community/tutorials/how-to-install-mongodb-on-ubuntu-16-04

Thanks for your hard work !