Normalize each remove argument with determine_image() before building
the RemoveImage request. Relative paths are converted before reaching
portabled.
Reproducer:
cd /tmp
portablectl remove ./portable-repro
Before:
./portable-repro was sent unchanged to portabled and rejected as an
invalid image name/path. Removing an image by a relative path failed
even though the path referred to a valid local image.
Follow-up: 61d0578b07