WIP: templates: Add node.openshift.io/rhelmajor label, drop os_version one

[cgwalters]

This removes the functionality added in
#514
which I don't think really worked for what people needed; a node
selector can't parse the value.

All we care about is currently 7 or 8; this signals things like
iptables vs nftables.

And the presence of this label also signals "RHEL" too;
though we keep the os_id label in case e.g. a daemonset should only
run on RHCOS (or traditional RHEL).

Closes: #582

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[cgwalters]

Haven't done full testing of this yet, submitting WIP for visibility/early review.

[kikisdeliveryservice]

to clarify, if:

• rhelmajor = 7|8 then os_id = nil
• os_id != nil then rhelmajor = nil

?

[cgwalters]

to clarify, if:

Mmm, os_id is always set as it was before, I haven't changed that (right?). We will either have os_id=rhcos or os_id=rhel.

[kikisdeliveryservice]

@cgwalters thanks, got it!

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[cgwalters]

OK so I discovered this: --node-labels mapStringString <Warning: Alpha feature> Labels to add when registering the node in the cluster.

In other words, the labels aren't dynamic which is rather problematic for something that has a version number. I think the MCD should probably start managing the labels.

[cgwalters]

Obsoleting in favor of #657