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?

Did you also try the option to use the username as the hash key? that way you can ommit the array. Like so:
```
"sysadmins": {
  "<username_1>": {
    "password": "<hashed password: openssl passwd -1 'plaintextpassword'>",
    "ssh_keys": [
      "ssh-rsa AAA123...xyz== foo",
      "ssh-rsa AAA456...uvw== bar"
    ]
  },
  "<username_2>": {
    "password": "<hashed password: openssl passwd -1 'plaintextpassword'>",
    "ssh_keys": [
      "ssh-rsa AAA123...xyz== foo",
      "ssh-rsa AAA456...uvw== bar"
    ]
  }
}
```