renamed plugins to contrib (they are not really plugins)
rewrote README.md to reflect new usage
added new dir to setup.py so it gets copied with installation, in views
of making using inventory scripts easier in teh future

- auth_system
- region_name
- service_type

These are config settings that could be left out in many scenarios, but
the current code is requiring them. In particular, "service_type" is a
new one in PR #7444 so if we add that and don't set a default, then
existing .ini files won't work:

```
  File
"/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/ConfigParser.py",
line 618, in get
    raise NoOptionError(option, section)
ConfigParser.NoOptionError: No option 'service_type' in section:
'openstack'
```

The provisioning module knows more about how nova deals with IP
addresses now. Ensure that the inventory module is similarly as smart
by separating out the logic into the openstack/module_utils.

- auth_system
- region_name

These are config settings that could be left out in many scenarios, but
the current code is requiring them. With this in place, I can get by
with this minimal .ini file:

```ini
[openstack]
version=1.1
auth_url=http://{keystone_host}:5000/v2.0
project_id=web
username={username}
api_key={password}
```

@mpdehaan said that nothing uses them at
https://github.com/ansible/ansible/pull/7988#issuecomment-47600006

Signed-off-by: Hector Acosta <hector.acosta@gmail.com>