compositor-wayland: move output init into common, fix error path

Move the weston_output_init() call into wayland_output_create_common().
This avoids passing the name twice to different functions, and follows
the precedent set in "libweston: weston_output_init(..., +name)" for
calling init before accessing fields.

Since the error paths in wayland_output_create_for_parent_output() and
wayland_output_create_fullscreen() are now guaranteed to have
weston_output init'd, call weston_output_destroy() appropriately. There
might be more to free than just the name.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>