Why are all of the group names in lists? Looking the `get_group_name` function in buildbot.py
```
def get_group_name(name):
   """Get the group name, if this test has a group."""
   for group in GROUP_NAMES:
      if name in GROUP_NAMES[group]:
         return group
   return "unknown"
```
The `if name in GROUP_NAMES[group]:` will have a time complexity of O(N), If the names we're stored in a dict we could get O(1). Is there a requirement that the lookup be performed in a certain order?