lxc init doesn't immediately fail on duplicated instance name if the source image is not cached #12554
Description
If you already have an instance named foo, trying to created another one with the same name will not immediately fail if the source is not cached.
Steps to reproduce:
$ fingerprint="$(lxc image list -f csv -c lf ubuntu-daily:24.04 type=container | head -n1 | cut -d, -f2)"
$ lxc init "ubuntu-daily:$fingerprint" foo # create instance and populate local image cache
Creating foo
$ lxc init "ubuntu-daily:$fingerprint" foo # fail early, good
Creating foo
Error: Failed creating instance record: Add instance info to the database: This "instances" entry already exists
$ lxc image delete "local:$fingerprint" # remove the locally cached image
$ lxc init "ubuntu-daily:$fingerprint" foo # fails late after retrieving the image
Creating foo
Retrieving image: metadata: 100% (1.21GB/s)
Retrieving image: rootfs: 1% (2.86MB/s)
...
Error: Failed creating instance record: Add instance info to the database: This "instances" entry already exists
Ideally, the check for duplicated name should be done prior to doing the expensive image fetch.