wkb-ibus: Fix repeatly create ibus-daemon.

It is possible that the ibus-daemon is up but weekeyboard can't
get anything from it. In this case, weekeyboard will always create
a new ibus-daemon. This patch fix it.

Change-Id: If7cb00345971769c3f95b54e74f723013835514d
Signed-off-by: Alex Wu <zhiwen.wu@linux.intel.com>