nixos-install: Pass CA cert bundle to chroot.

Since we're using HTTPS for the binary cache (introduced in faf0797) by
default, the binary cache should also be available during installation.

The file that is defined in SSL_CERT_FILE outside of the chroot is
copied over to /tmp/ca-cert.crt inside the chroot, so we have an
absolute path we can reference during nixos-install. However, this might
end up with the file not being cleaned up properly from outside of the
store, but neither would be /tmp/root so the cleanup issue needs to be
solved in another place (or commit to be more exact).

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
(cherry picked from commit cf7f15c92ca07d2d6d249fd2965b9e1950fb11a5)
Signed-off-by: Domen Kožar <domen@dev.si>
virtualbox: Allow disabling the network interface.

The current nixos module for VirtualBox unconditionally configures a vboxnet0
network interface at boot. This may be undesired, especially when the user wants
to manage network interfaces in a centralized manner.

(cherry picked from commit 9fa2c35ec8199951f217296e40f534c1e2e0f336)
Signed-off-by: Domen Kožar <domen@dev.si>
virtualbox: Unbreak the nixos module.

(cherry picked from commit 65393ca8d3b959657e16e402a3db3ac8f1fdb6ed)
Signed-off-by: Domen Kožar <domen@dev.si>
redmine: use libc libciconv implementation on Linux.

(cherry picked from commit 32f9644943e8772b33a58a4f7105b3dc7f38723d)
Signed-off-by: Domen Kožar <domen@dev.si>