Fix weston-launch

Add a patch to weston-launch which makes it use the user's login shell.
Patch lifted from:
http://git.sardemff7.net/wayland/weston/commit/?h=wip/shell-fix&id=d53cf5bd980196147189a30caa54d375156c7a12

After this change weston-launch works again. From console TTY. Currently
launching from SSH session does not work.