Accept-invites script doesn't join all rooms

Sometimes, after running the locust-accept-invites script, we still have lots of users with pending invites in the main "chat" test. It seems the problem happens when there are invites that the server does not include in the initial /sync response.

So it seems like the fix is that we need to sync more than once in the "accept invites" script.

Something like this:

done = False
while not done:
    sync()
    if len(invites) < 1:
        done = True
    else:
        accept_invites()