Build weston-clients to weston-ivi-shell

In order to run weston-clients on weston-ivi-shell, weston-clients
should be built in weston-ivi-shell package.

Change-Id: Ic4ac3cd9896bf3dbf112919226d55516605de994
Signed-off-by: Xiong Zhang <xiong.y.zhang@intel.com>