shadow_utils: make shadow --root work by fake permissive mode

[praiskup]

Fixes: #1285

[praiskup]

While the use of --root is desired and safer than --prefix, I'm not convinced we want to apply the needed SELinux workaround. I'd rather wait till shadow-utils people tell us what to do about this.

[xsuchy]

This does not work for me. When I change it from host, then it is remounted. And it is read only, so I cannot change it from chroot neither.

[praiskup]

Yes, Mock's selinux plugin has some hacks related to SELinux too, and we do recursive bind-mounts later:

mock/mock/py/mockbuild/mounts.py

Lines 228 to 231 in db64d46

	BindMountPoint(srcpath=mount_point,
	bindpath=host_path,
	recursive=True,
	options="nodev,noexec,nosuid,readonly,rprivate"),

The point of this hack is to prepare the enforce file right before shadow-utils (useradd, groupadd, etc.) are executed (from /usr/sbin on host).