When --with-system-qemu is used, it is possible that we cannot find
qemu-system-i386 in LIBEXEC_BIN, which can cause error in xencommons
init script and xen-qemu-dom0-disk-backend.service systemd service.
Signed-off-by: Ting-Wei Lan <lantw44@gmail.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>