[lxd] Multipass not reacting correctly with internally shut down instances

[townsend2010]

if you don't use multipass stop, then it's really hard for multipassd to know the state of a VM. That said, we could probably be better at detecting instance states that are modified outside of Multipass when using the LXD driver.

@townsend2010 are you aware that multipass stop --all is not enough to prevent instances from auto-booting the next time the host boots?

Example:

• An instance is powered off internally, using a command like poweroff
• multipass stop --all is run on the host machine.
• Host machine is rebooted, and the instance (unfortunately!) auto-boots, despite both above attempts to prevent that :/

(This should be easily fixable, no?)

PS This is separate from the question as to whether or not Multipass will one day act like a modern BIOS:

there really should be a Multipass/LXD option (rather like in a PC's BIOS/firmware) allowing you to toggle between either of these 2 choices:

1. Auto-boot VM's/instances after power failure / glitch / etc.
2. Do NOT auto-boot VM's/instances after power failure / glitch / etc.

Originally posted by @holta in #2610 (comment)