NodePublishVolume test doesn't set volume attributes returned by CreateVolume

[msau42]

The CSI spec is a little confusing. It says that the VolumeAttributes field is optional, but must match the attributes of the volume:

       // Attributes of the volume to publish. This field is OPTIONAL and  
        // MUST match the attributes of the Volume identified by                               
        // `volume_id`.                   
        VolumeAttributes     map[string]string 

[saad-ali]

The intention is that if it is returned by the volume plugin on a CreateVolumeResponse it must be passed on on subsequent PublishVolume requests. csi-test should verify this behavior, and optionally we should clarify the wording of this in the spec.

[msau42]

/assign