Force the SELinux user during relabel operation (530192)

When Portage relabels the files of the package, it currently calls
setfiles (which is correct) but does not use the -F option (force). As a
result, the files only get assigned the right SELinux type, but not the
right SELinux user and SELinux role.

By using "setfiles -F", the SELinux user (and role, but role almost
always remains "object_r") is set to the right one (system_u mostly).

Without this, a multi-user system with different SELinux users and with
User Based Access Control (UBAC) enabled (the local "ubac" USE flag)
might find that some software fails to work for different SELinux users
than the one used to install the software, until a full forced relabel
operation is done.

X-Gentoo-Bug: 530192
X-Gentoo-Url: https://bugs.gentoo.org/show_bug.cgi?id=530192
Acked-by: Zac Medico <zmedico@gentoo.org>