Add albatross user and allow user into the group to use albatross

[dinosaure]

It's a small improvement but when we want to install albatross, my configuration is like:

• I have an user mirage
• The script should create the albatross user
• mirage can be a part of the albatross group
• mirage should be allowed to use sockets

This patch allows the albatross group to use sockets and create the required albatross user for the installation. In the opposite, the daemon fall back as a root user and sockets got permissions only for the root user.

[hannesm]

Thanks, I merged this manually and adapted the useradd (by specifying home, login shell, and also create a group).