## Bug description

This is what a default feature flag looks like:
<img width="577" alt="empty feature flag" src="https://user-images.githubusercontent.com/4550621/113333154-63f36a00-9322-11eb-8fb0-71b0cd865181.png">
It has no rollout percentage specified, nor filters, so it says "Rolling out to 100% of users". However I've experienced that in fact in this situation the flag is rolled out to *nobody*.

CC @paolodamico 

## Expected behavior

Flag should work the way it says.

## How to reproduce

1. Create a feature flag and leave it as is, supposedly completely rolled out.
2. Try to use it.
3. Discover that the flag is not rolled out.

## Environment

- [x] PostHog Cloud
- [x] self-hosted PostHog, version/commit: master (8f4ae2b)

#### *Thank you* for your bug report – we love squashing them!

posthog/models/feature_flag.py
return self.get_filters().get("groups", [])
    def get_filters(self):
        if "groups" in self.filters:
            return self.filters
        else:
            
            
            return {
                "groups": [
                    {"properties": self.filters.get("properties", []), "rollout_percentage": self.rollout_percentage}
                ]
            }
class FeatureFlagMatcher:
    def __init__(self, distinct_id: str, feature_flag: FeatureFlag):
        self.distinct_id = distinct_id
        self.feature_flag = feature_flag
    def is_match(self):
        return any(self.is_group_match(group, index) for index, group in enumerate(self.feature_flag.groups))
    def is_group_match(self, group: Dict, group_index: int):
        rollout_percentage = group.get("rollout_percentage")
        if len(group.get("properties", [])) > 0:
            if not self._match_distinct_id(group_index):
                return False
            elif not rollout_percentage:
                return True
        if rollout_percentage is not None:
            if self._hash <= (rollout_percentage / 100):
                return True
        return False
    def _match_distinct_id(self, group_index: int) -> bool: