Changed 'contents' to 'contents_pillar' to correctly parse newlines for private/public SSH keys.

this pillar file will generate an error:
```
--- 
users: 
  foo: 
    name: foo
    shell: /bin/false
    ssh_keys: 
      privkey: |
        -----BEGIN RSA PRIVATE KEY-----
        foo
        -----END RSA PRIVATE KEY-----
      pubkey: "ssh-rsa somekey foo@bar.com"
```

error:
```
    Data failed to compile:
----------
    Rendering SLS "base:users" failed: Unknown yaml render error; line 52

---
[...]
    - user: foo
    - group: foo
    - mode: 600
    - contents: -----BEGIN RSA PRIVATE KEY-----
foo <======================
```

The solution is to use contents_pillar (0.17.0+).