## 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
class Meta:
        constraints = [models.UniqueConstraint(fields=["team", "key"], name="unique key for team")]
    key: models.CharField = models.CharField(max_length=400)
    name: models.TextField = models.TextField(
        blank=True,
    )  
    filters: JSONField = JSONField(default=dict)
    rollout_percentage: models.IntegerField = models.IntegerField(null=True, blank=True)
    team: models.ForeignKey = models.ForeignKey("Team", on_delete=models.CASCADE)
    created_by: models.ForeignKey = models.ForeignKey("User", on_delete=models.CASCADE)
    created_at: models.DateTimeField = models.DateTimeField(default=timezone.now)
    deleted: models.BooleanField = models.BooleanField(default=False)
    active: models.BooleanField = models.BooleanField(default=True)
    def distinct_id_matches(self, distinct_id: str) -> bool:
        return FeatureFlagMatcher(distinct_id, self).is_match()
    def get_analytics_metadata(self) -> Dict:
        filter_count = sum(len(group.get("properties", [])) for group in self.groups)
        return {
            "groups_count": len(self.groups),
            "has_filters": filter_count > 0,
            "has_rollout_percentage": any(group.get("rollout_percentage") for group in self.groups),
            "filter_count": filter_count,
            "created_at": self.created_at,
        }
    @property
    def groups(self):