Drop the * operator from a function call

The `*` operator is a useful tool, but it's also fairly mysterious. Use
`chain.from_iterable` instead.

The methods which use the affected constant should not be affected:

```
$ nosetests tests/foreman/api/test_permission.py -m test_search_permissions
.
----------------------------------------------------------------------
Ran 1 test in 1.096s

OK
$ nosetests tests/foreman/api/test_permission.py -m test_search_by_name
................................................................................................................................................................................................................
----------------------------------------------------------------------
Ran 208 tests in 89.741s

OK
```

A quick test shows that the transformation should be valid:

```python
>>> t1 = tuple(chain(*PERMISSIONS.values()))
>>> t2 = tuple(chain.from_iterable(PERMISSIONS.values()))
>>> t1 == t2
True
```