export to simplestreams

[melato]

Facilitate exporting images and adding them to a simplestreams directory.

The incus-simplestreams program can add an exported image to a simplestreams directory.

incus-simplestreams requires the image root to be in the squashfs format and the metadata.yaml, templates/ to be in a tar.xz file. But if an incus image is created by "incus publish" and then exported with "incus image export", it is exported as a single tar.gz file.

So, the first step is to convert the tar.gz file to a rootfs.squashfs and metadata.tar.xz files.

[melato]

I made several changes to lxops to facilitate this:

• convert images from unified to split tarballs
• export image from incus to split tarball format
• update metadata.yaml
• incus-simplestreams wrapper

But I reverted all these changes, and left only one:

• add options to "lxops publish" to set image properties This is just a wrapper to "incus publish". It was needed only by someone who uses both LXD and Incus, in order to avoid hardcoding "lxc" or "incus" in scripts.