Bernie's build system workflow proposal

The labels are build stream names, and they're intended to be used much like git repositiories: anyone can create their own as needed, and maintainers can pull/push between them.

 +-----+ +-----+ +------+ +------+
 |marco| |tomeu| |bernie| |mstone| (unstable trees)
 +-----+ +-----+ +------+ +------+
    |       |       |        |
    v       v       |        |
   +---------+      |        |
   |  sugar  |      |        | . . (pull)
   +---------+      |        |
        |           |        |
        V           V        V
   +- - - - - - - - - - - - - -+
   |          testing          |  (kim, jim, walter, alex)
   +- - - - - - - - - - - - - -+
                |
                V
   +---------------------------+
   |          stable           |
   +---------------------------+