weston-init: start weston on a new VT

weston-init: start weston on a new VT

Weston 1.3 needs to run on a VT, which is typically handled by weston-launch.
Currently weston-init doesn't use weston-launch as that depends on the
(non-default) pam DISTRO_FEATURE, so depend on kbd and use openvt directly.

This also fixes problems caused by the init script blocking until Weston exits,
which meant that later init scripts were not actually running.

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>