Moved zypper repo_types into __init__ method

Having this at the class-level was causing tracebacks at import time.

Fixes the following traceback:

```python
Traceback (most recent call last):
  File "/Users/shouse/src/salt/salt/salt/loader.py", line 897, in load_modules
    ), fn_, path, desc
  File "/Users/shouse/src/salt/salt/salt/modules/zypper.py", line 212, in <module>
    class _RepoInfo(object):
  File "/Users/shouse/src/salt/salt/salt/modules/zypper.py", line 218, in _RepoInfo
    zypp.RepoType.NONE_e: 'NONE',
NameError: name 'zypp' is not defined
```