Don't allow mixing "multiple-egress-IP HA" with "auto-allocated-egress-IP HA"

[danwinship]

We now have two different ways to do egress IP HA:

1. Assign multiple egress IPs to a NetNamespace, so that if the node hosting the first one goes down, we switch to using the second one.
2. Use fully-automatic allocation with egressCIDRs, and let the master move the egress IP between nodes if one node goes down.

So clearly someone's going to say "oh boy, I'll use both and then get twice as much high availability!" This is a terrible idea because what will actually happen is:

1. Everyone will be happily using egress IP 1 on node 1
2. Node 1 goes down
3. Nodes notice that egress IP 1 has stopped responding and switch to using egress IP 2
4. The master notices that node 1 has gone down and moves egress IP 1 to a different node
5. Nodes notice that egress IP 1 has started responding again and switch back

So you get twice as much disruption as you would have gotten if you were only using one of the two forms of HA. So this fixes it so that we don't do auto-allocation for egress IPs that are being used as part of multiple-egress-IP HA.

[dcbw]

/lgtm

[dcbw]

/retest

[openshift-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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[openshift-bot]

/retest

Please review the full test history for this PR and help us cut down flakes.

[openshift-bot]

/retest

Please review the full test history for this PR and help us cut down flakes.