1) Modify dependencies
Add dependencies required for to be able use containers created from
"images.linuxcontainers.org". Several of them require "lxc-attach" for set
password so to be able login. None of them has SSH preinstalled so
"lxc-console" is required to be able login and install SSH, for example.
Remove dependency "xz", it seems incompatible with LXC_BUSYBOX_OPTIONS when
both are enabled happens a build crash.
2) Change container image repository
The repository "virtualwrt.org/containers/" seems to not work, I have change
it by the official LXC container image repository.
3) Translate the arch
Translate the local uname architecture to a valid "images.linuxcontainers.org"
arch. Only tested with the platform "mvebu" (armv7l -> armhf).
4) Other minor fixes
Use same server to list images and download the image.
Disable GPG check when listing images.
Reported-by: "Admin Localnet <localnet@users.noreply.github.com>"
[Squashed commits, cleaned up whitespace, refactor arch mapping, escape url
setting, use system wide ubus helper, use uci model library]
Closes: #1422
Signed-off-by: Jo-Philipp Wich <jo@mein.io>
