Container execution fixes and refactors

The main gist here is that we should only ask for a pseudoterminal in the child podman/docker process when we want to run interactively, i.e. use the --tty CLI option of either engines. This is needed to proceed further with https://listman.redhat.com/archives/libvir-list/2023-August/241471.html where during review it was suggested that we should use test -d 1 inside the project's build script. That's a valid request which however can't be addressed until we make proper changes in lcitool where we should be definitely able to determine whether we're simply just running a script non-interactively in a container environment or have a shell session inside a container.