upgraded: link dynamically, chroot during exec

upgraded: link dynamically, chroot during exec

The chroot ensures we don't reference anything on the rootfs and is
reverted after the upgraded exec. While we're at it, also improve error
handling a bit.

This change also required changes to sysupgrade, as the dynamically linked
version is expected at a different location, and libraries need to be made
available.

Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>