Snapcraft LXD container configuration

[kalikiana]

@sergiusens

Configuration

We are at a point where it would be wise to introduce configuration to snapcraft in a global and per project manner. Things like selecting the default lxd remote to use or the fact that you want persistent containers assigned to a project by default are worthy of having.

This is also going to be useful, specifically in the case of containers, to have default proxies setup, either in the case of needing one at all to talk to the outside or setting up one for a package repo in particular. You don’t want to be doing this every time you start a new project.

Snapcraft should read and write a file like .snapcraft and use it to keep track of the answers to UI prompts.

[elopio]

A few things to note before we start implementing the config:

• There’s already a file in $HOME/.config/snapcraft/snapcraft.cfg where we save the macaroon.
• There’s also .snapcraft/travis_snapcraft.cfg created by the enable-ci command, to save the attenuated macaroon that allows to release only to edge.
• We have just added a snap/.snapcraft directory for global state.
• There are quite a few things called config in our source code: $ grep -r config snapcraft/. A cleanup on the source code to clarify the concepts would be nice.