netbase: add entry to /etc/hosts according to /etc/hostname

netbase: add entry to /etc/hosts according to /etc/hostname

We default hostname to ${MACHINE}, but it's not in /etc/hosts,
resulting in commands like `hostname -f' failing due to lack
of entry.

So add entry to /etc/hosts according to /etc/hostname. We do
this via pkg_postinst because hostname is set in base-files
recipe.

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>