Use osusergo build tag for static build
Use osusergo build tag for static build

We now use the osusergo build tag to not use the glibc functions which
occur in the warnings but them from golang the os/user package.

Signed-off-by: Sascha Grunert <70ab469ddb2ac3e35f32ed7c2fd1cca514b2e879@suse.com>

mtrmac/skopeo,mtrmac/skopeo,mtrmac/skopeo