Make OrderedDict private (_OrderedDict) in pkg state

As it is, OrderedDict shows up in things like sys.list_state_functions:

```
root@localhost:~# salt '*' sys.list_state_functions pkg
myminion:
    - pkg.OrderedDict
    - pkg.installed
    - pkg.latest
    - pkg.mod_aggregate
    - pkg.mod_init
    - pkg.purged
    - pkg.removed
    - pkg.uptodate
```