lcitool: fix compat with podman 4.4.0 and docker

Daniel P. Berrangérequested to merge
berrange/libvirt-ci:podman-json into master

The '{{ json . }}' syntax has returned a single JSON document with an array of entries for images historically with podman.

Since podman 4.4.0 this now returns a concatenation of JSON documents, one document per image. Our code is not able to parse a concatenation of documents.

This was done to fix docker compatibility[1], because

{{ json .}}

was supposed to be equivalent to

{{ . | json }}

while podman mistakenly made it equivalent to

{{ json }}

IOW, we were already broken in terms of docker compat too.

Since we want the single document, we need to use plain 'json' or '{{ json }}'. This picks the former since it does not appear we have a need to use any advanced features of the Go template syntax.

[1] https://github.com/containers/podman/issues/16436 Signed-off-by: Daniel P. Berrangé berrange@redhat.com

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