Refactor things to use explicit names, and put in a trap to cleanup
after any errors.
Currently, if the build/run/export steps fail, it leaves behind images
which eventually clog things to the point podman won't run any more
(see also https://github.com/containers/podman/pull/12233 about errors
seen due to this)
Change-Id: Ib328a07ad67e3f71f379fbf34ae7ef74e212ef1c