sdk.py: fix moving dnf contents

The dnf contents should be moved to <host_sysroot>/etc/dnf/xxx
instead of just <host_sysroot>/etc.

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 74b78d16)
Signed-off-by: Steve Sakoman <steve@sakoman.com>