Let BuildManager check out branches

[Jeroen T. Vermeulen]

For regenerating templates from bzr branches using the buildfarm, we'll have to extend BuildManager to be able to check out a branch. This will also require extra networking permissions for the slave.

(The assumption for now is that we won't generate templates from private branches; that'd require sending the individual source files across, which is a pain. Plus it might give away the source code's secrets, so probably not a good idea anyway).

The PPA builders will need http access to production codehosting (bazaar.lp.net) and xml-rpc server in order to be able to generate translation templates from branches. Specific ports that need opening are bazaar.launchpad.net/80 and xmlrpc.edge.launchpad.net/443

[Jeroen T. Vermeulen (jtv)]

As per bug 523467 we're first making it possible to get a public URL for a branch specifically using http (instead of whatever protocol the branch happens to use).

[Данило Шеган (danilo)]

This is about setting up firewall rules to allow access to hosted bazaar branches from build farm slaves. We'll need to test it on dogfood first, but to be able to test it, we need to make our jobs try accessing it with bug 520651.