Automatic merge from submit-queue
validate third party resources
addresses validation portion of https://github.com/kubernetes/kubernetes/issues/22768
* ThirdPartyResource: validates name (3 segment DNS subdomain) and version names (single segment DNS label)
* ThirdPartyResourceData: validates objectmeta (name is validated as a DNS label)
* removes ability to use GenerateName with thirdpartyresources (kind and api group should not be randomized, in my opinion)
test improvements:
* updates resttest to clean up after create tests (so the same valid object can be used)
* updates resttest to take a name generator (in case "foo1" isn't a valid name for the object under test)
action required for alpha thirdpartyresource users:
* existing thirdpartyresource objects that do not match these validation rules will need to be removed/updated (after removing thirdpartyresourcedata objects stored under the disallowed versions, kind, or group names)
* existing thirdpartyresourcedata objects that do not match the name validation rule will not be able to be updated, but can be removed
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