Code review comment for lp:~jml/launchpad/db-distro-level-ppa-privacy

I've spoken with sinzui on IRC. In a nutshell, here's the behaviour we want

 1. if the team owning the PPA is private, and you're in the team:
   a) you are allowed to create a private PPA
   b) you are not allowed to create a public PPA

 2. if you are allowed to create private things on LP, then you are be allowed to create private PPAs for public teams

   * "you are allowed to create private things" == you.checkAllowVisibility()
   * True if admin, commercial admin or they have a commercial subscription
   * used currently for whether to show checkbox on private teams

 3. otherwise, you are not allowed to create private PPAs

This does not require a database patch and does not require a celebrity. I'll proceed with this implementation approach on Monday if I don't hear otherwise.