lib: fix multiple rootfs entries
lib: fix multiple rootfs entries

acirenderer adds a rootfs entry since
https://github.com/appc/spec/pull/437

Hence, we need to ignore it because we write our own rootfs entry.

appc/docker2aci,vishvananda/docker2aci,appc/docker2aci,jsoriano/docker2aci,OMWAVE/docker2aci,dgonyeo/docker2aci,OMWAVE/docker2aci,jsoriano/docker2aci,dgonyeo/docker2aci,iaguis/docker2aci,jonboulle/docker2aci,vishvananda/docker2aci