`security.devlxd.images` regressed somewhere after `5.0`

[simondeziel]

5.0/edge shows a super fast download indicating it was pulling from the parent LXD. 5.21/edge shows the image download speed to indicating a download from the Internet. latest/edge shows similarly slow download indicating a download from the Internet.

The tests/cluster should always have u1 image downloaded from the parent LXD as the test is using the same image for both the parent and child instances.

[MusicDin]

Is security.devlxd also enabled or just security.devlxd.images? The latter should not have effect if security.devlxd is disabled or empty.

[MusicDin]

Ignore me.. The latter should have no effect only if security.devlxd is false

[markylaing]

Closed via https://github.com/canonical/lxd/pull/13730