Allow multiple records per A record in OpenStack Designate Provider

[hikhvar]

Description

Allow multiple records per A record. Therefore update the Delete and Create order so, we don't delete a single old record value.
Before this patch, external-dns alternated between two IPs as record values if upgraded from a single record to two A records.

Fetch labels from existing TXT records to fix https://github.com/kubernetes-sigs/external-dns/issues/

Fixes #603

Checklist

• Unit tests updated
• End user documentation updated

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/lifecycle stale

[hikhvar]

/remove-lifecycle stale

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The Kubernetes project currently lacks enough contributors to adequately respond to all PRs.

This bot triages PRs according to the following rules:

• After 90d of inactivity, lifecycle/stale is applied
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/lifecycle stale

[frittentheke]

@Raffo @njuettner would be awesome to have this addition in the Designate provider. Could you kindly look into this change?

[frittentheke]

/remove-lifecycle stale

[szuecs]

/approve
/lgtm

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hikhvar, szuecs

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