Fix NM config

/etc/resolv.conf/ symlink is created by NM at first boot (still cannot pin point the root cause, may be a internal SUSE symlink related to NM version which is newer than the one used for LeapMicro 6.0). The quick workaround is to create a physical, empty stub file during the KIWI build process. Because NetworkManager sees a physical file already exists, it will not attempt to drop its internal symlink. Then, it will successfully read 10-dns.conf file and overwrite that physical stub with real DNS servers.

Close #46 (closed)

Fix tested here sylva-projects/sylva-core!6798 (merged)