launcher-util: Force all weston_launcher_open()s to use O_CLOEXEC

launcher-util: Force all weston_launcher_open()s to use O_CLOEXEC

Really, there's pretty much no time we'd ever want O_CLOEXEC unset,
as it will likely result in leaking fds to processes that aren't
interested in them or shouldn't have them.

This also removes the (now unused) code from weston_logind_open() that
could drop O_CLOEXEC.

Signed-off-by: Derek Foreman <derekf@osg.samsung.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>