base-files: move hostname operations out of issue file settings

base-files: move hostname operations out of issue file settings

The function do_install_basefilesissue is meant to deal with
/etc/issue* files and the following setting could actually be
overridden.

  BASEFILESISSUEINSTALL ?= "do_install_basefilesissue"

So move the hostname operations out of this function.

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