update-rcd.bbclass: fix host/target test

"update-rc: Stop and remove service if updating package" (oe-core d91b08) had a
bug in it's implementation of a "host or target" test which always resulted in
"target", so the rootfs scripts were attempting to restart daemons on the host.

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