each dev in host_devs[] should be waited in initqueue to make sure they
are oneline before initqueue finish.
Add a new wait_host_devs.sh in base module to make this a generic thing.
Because all the devs in fstab lines are also added to host_devs, so no need
do same wait in fstab-sys module anymore.
[v2->v3]: do not add slave devices to host_devs
wait for persistent dev name in initramfs
Signed-off-by: Dave Young <dyoung@redhat.com>