allow anonymous usage for public APIs like GET /teamMembers/{id}

In we create a Lambda that needs to list the members of a Team. The Lambda has no Synapse credentials so it can't call Synapse.login(). It needs to call Synapse.getTeamMembers() which uses an anonymous service to list the members of a team. (This is public information.). Currently the Python client requires logging in before making any requests. So The Lambda can't use getTeamMembers().