recipes-connectivity/samba: Only rmdir directories that exist

Depending on PACKAGECONFIG selection, the /run/samba directory may not
have been created. Make the do_install_append handle both situations
by checking whether these directories exist before attempting to remove
them.

This fixes do_install failing with an error like this:
 rmdir: failed to remove '/.../samba/4.1.12-r0/image/run/samba': No such file or directory

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>