Improve the check for KUDO CRDs when creating a client

[nfnt]

What this PR does / why we need it:
CRDs aren't tied to a namespace. By checking for them directly through the 'apiextensions' client is a cleaner approach than checking if listing CRDs objects succeed. This also make the namespace parameter of kudo.NewClient redundant.

[alenkacz]

LGTM

[nfnt]

Going to check if this CI failure is a flake or actually caused by the change:

Failed
logger.go:37: 14:55:11 | create-or-update | Creating namespace: kudo-test-careful-wolf
logger.go:37: 14:55:11 | create-or-update/0-crd | starting test step 0-crd
logger.go:37: 14:55:11 | create-or-update/0-crd | CustomResourceDefinition:/prowjobs.prow.k8s.io created
logger.go:37: 14:55:41 | create-or-update/0-crd | test step failed 0-crd
case.go:154: --- CustomResourceDefinition:/prowjobs.prow.k8s.io
    +++ CustomResourceDefinition:/prowjobs.prow.k8s.io
    @@ -2,18 +2,123 @@
     kind: CustomResourceDefinition
     metadata:
       name: prowjobs.prow.k8s.io
    +spec:
    +  additionalPrinterColumns:
    +  - JSONPath: .spec.job
    +    description: The name of the job being run.
    +    name: Job
    +    type: string
    +  - JSONPath: .status.build_id
    +    description: The ID of the job being run.
    +    name: BuildId
    +    type: string
    +  - JSONPath: .spec.type
    +    description: The type of job being run.
    +    name: Type
    +    type: string
    +  - JSONPath: .spec.refs.org
    +    description: The org for which the job is running.
    +    name: Org
    +    type: string
    +  - JSONPath: .spec.refs.repo
    +    description: The repo for which the job is running.
    +    name: Repo
    +    type: string
    +  - JSONPath: .spec.refs.pulls[*].number
    +    description: The pulls for which the job is running.
    +    name: Pulls
    +    type: string
    +  - JSONPath: .status.startTime
    +    description: When the job started running.
    +    name: StartTime
    +    type: date
    +  - JSONPath: .status.completionTime
    +    description: When the job finished running.
    +    name: CompletionTime
    +    type: date
    +  - JSONPath: .status.state
    +    description: The state of the job.
    +    name: State
    +    type: string
    +  conversion:
    +    strategy: None
    +  group: prow.k8s.io
    +  names:
    +    kind: ProwJob
    +    listKind: ProwJobList
    +    plural: prowjobs
    +    singular: prowjob
    +  preserveUnknownFields: true
    +  scope: Namespaced
    +  validation:
    +    openAPIV3Schema:
    +      properties:
    +        spec:
    +          properties:
    +            max_concurrency:
    +              minimum: 0
    +              type: integer
    +            type:
    +              enum:
    +              - presubmit
    +              - postsubmit
    +              - periodic
    +              - batch
    +              type: string
    +        status:
    +          anyOf:
    +          - not:
    +              properties:
    +                state:
    +                  enum:
    +                  - success
    +                  - failure
    +                  - error
    +                  - aborted
    +                  type: string
    +          - required:
    +            - completionTime
    +          properties:
    +            state:
    +              enum:
    +              - triggered
    +              - pending
    +              - success
    +              - failure
    +              - aborted
    +              - error
    +              type: string
    +  version: v1
    +  versions:
    +  - name: v1
    +    served: true
    +    storage: true
     status:
       acceptedNames:
         kind: ProwJob
    +    listKind: ProwJobList
    +    plural: prowjobs
    +    singular: prowjob
       conditions:
    -  - message: no conflicts found
    +  - lastTransitionTime: "2019-11-07T14:55:11Z"
    +    message: no conflicts found
         reason: NoConflicts
         status: "True"
         type: NamesAccepted
    -  - message: the initial names have been accepted
    +  - lastTransitionTime: null
    +    message: the initial names have been accepted
         reason: InitialNamesAccepted
         status: "True"
         type: Established
    +  - lastTransitionTime: "2019-11-07T14:55:11Z"
    +    message: '[spec.validation.openAPIV3Schema.properties[spec].type: Required value:
    +      must not be empty for specified object fields, spec.validation.openAPIV3Schema.properties[status].anyOf[0].not.properties[state].type:
    +      Forbidden: must be empty to be structural, spec.validation.openAPIV3Schema.properties[status].type:
    +      Required value: must not be empty for specified object fields, spec.validation.openAPIV3Schema.type:
    +      Required value: must not be empty at the root]'
    +    reason: Violations
    +    status: "True"
    +    type: NonStructuralSchema
       storedVersions:
       - v1
     
    
case.go:154: resource CustomResourceDefinition:/prowjobs.prow.k8s.io: .status.conditions: slice length mismatch: 2 != 3
case.go:157: failed in step 0-crd
logger.go:37: 14:55:41 | create-or-update | create-or-update events from ns kudo-test-careful-wolf:
logger.go:37: 14:55:41 | create-or-update | Deleting namespace: kudo-test-careful-wolf

[nfnt]

The issue mentioned above will be fixed in #1039 and is unrelated to this diff.