Consider switching from using the LXD CLI to pylxd

[lengau]

What needs to get done

Replace most usage of the lxc and lxd CLI with pylxd.

Why it needs to get done

This is a faster, more reliable way to interact with LXD (e.g. #535)

[mr-cal]

I recall there was a decision to not use pylxd. It was prior to me joining and it's not documented. @cmatsuoka or @sergiusens - do you recall?

[lengau]

Thanks for that context @mr-cal. I've updated the title to represent that this should be a consideration, as if pylxd hasn't fixed these issues in the intervening years it's a null point

[mr-cal]

Here's the history: Craft-providers was written with the intent to support remote LXD servers. pylxd didn't support that when craft-providers was created, so we created our own abstraction layer around LXD.

[lengau]

Given our own slow progress on remote LXD instances, I wonder if helping pylxd to support remotes would be a reasonable way to do it.