Make API test_multiple_paths green again

Update OperatingSystem entity and map remote to local paths
Update str_type parameter in Role entity name field
Improve StringField to convert to a tuple if a string is given as
str_type
Improve skip_if_sam helper method to deal with entities modified by
functools.partial

Related to #1452
I have grabbed that snippet from:

```
if ((entity.func if isinstance(entity, partial) else entity) in
        BZ_1118015_ENTITIES and bz_bug_is_open(1118015)):
    self.skipTest('Bugzilla bug 1118015 is open.')
```

And the tests results shows that it really works