Explicitly install lxc on Ubuntu (fixes #101)

[carmstrong]

See #101 and #100.

[bflad]

I'm going to disagree with adding this to package recipe here, but would temporarily accept adding this to the lxc recipe. I can do this later tonight if I don't see an update to this PR. Docker introduced native execution driver support in 0.9 and made it the default, even though LXC has been the Docker way since 0.1.

I already have issues (like #91 for lxc) to migrate non-native execution driver functionality from this cookbook into cookbooks that will manage them much better. Otherwise we'd potentially have to support installation and configuration for LXC, libvirt, and others.

[carmstrong]

Agreed that it probably shouldn't be in the package recipe, at least without a conditional around it to check if lxc is indeed the exec_type. That was an oversight with my PR which I can fix.

However, the problem is that the lxc recipe is only included when the install_type != package, which it is by default. See: https://github.com/bflad/chef-docker/blob/master/recipes/default.rb#L14-L23

It actually looks like that's the fix - the docker::lxc recipe should indeed work, but it should be called outside the unless node['docker']['install_type'] == 'package' context.

[carmstrong]

@bflad this new commit works on a test-kicthen run, although I don't fully appreciate the implications of moving the include before include_recipe "docker::#{node['docker']['storage_driver']}" if node['docker']['storage_driver'] -- is it necessary to include the storage driver recipe before this?

[bflad]

We should be okay with its new placement. Thanks!

[bflad]

Please note that for Ubuntu this includes: https://github.com/hw-cookbooks/lxc/ from https://github.com/bflad/chef-docker/blob/master/recipes/lxc.rb#L9

[carmstrong]

Thanks @bflad! When the next version is cut, we'll update our dependencies.