imagebuildah: fix handling of destinations that end with '/'
imagebuildah: fix handling of destinations that end with '/'

Don't lose track of whether or not the specified destination for an ADD
or COPY instruction ends with the path separator, which is important.

Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>

Closes: #1620
Approved by: TomSweeneyRedHat

nalind/buildah,nalind/buildah-1,projectatomic/buildah,TomSweeneyRedHat/buildah,rhatdan/buildah,nalind/buildah-1,projectatomic/buildah,rhatdan/buildah,nalind/buildah-1,nalind/buildah,projectatomic/buildah,TomSweeneyRedHat/buildah,TomSweeneyRedHat/buildah,rhatdan/buildah