An untethered or uncompressed diskless boot downloaded the root image
only from the deployment server and retried it forever when that server
failed. Try the other managers that answered discovery as well, as the
tethered urlmount already does.
urlmount limits each small range request to 10 seconds, but the single
whole-image download cannot take a total limit. Give up on a connect
after 10 seconds and on a transfer that stalls for 30 seconds instead,
so a hung server moves on to the next one.
Centralize the SELinux chcon helper and use it for downloaded
systemd units, onboot hooks, and apiclient files across EL7 through EL10.
Include chcon in captured EL initramfs images.
Without this fix the onboot services failed to start on SELinux enabled
captured image.