Feature #79 sudo users

Another go at #79

It introduces a small cookbook "sysadmins" that takes sysadmins from the node json file and creates these on the server.

Please have a look and tell me what you think. If you like, I will add a commit that adds this cookbook to the base role and bump the version.

I could not find any tests in the main repo, but maybe I am looking wrong? Am I supposed to run/add tests? And if so, where?

We had a [discussion about this](https://github.com/intercity/chef-repo/pull/116#issuecomment-57094033) in the old PR.

TL;DR: since we cannot really oversee what the security-implications are of all choices, lets stick to The Ubuntu Default. Which is demand a password per user.

This is also the way the often-used [users::sysadmins cookbook](https://supermarket.getchef.com/cookbooks/users) works. (formerly known as LWRP-users).

The password is not stored plain-text, but rather the one-way hashed version. (Still: getting hold of this hashed password gives the attacker full access; it's just that he or she cannot read the actual password, this way)