availability zone is ignored when creating volume

[plribeiro3000]

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It seems that Fog ignores the value of the availability_zone parameter when creating OpenStack volumes. In https://github.com/fog/fog/blob/master/lib/fog/openstack/models/compute/volume.rb line 28 I would expect this argument to be passed to the create_volume call, but it's not.

If this is by design, for example because there are problems with the OpenStack API when using this feature, it should be documented; but I would currently consider this a bug.

Original issue opened by @dennis-sig at fog/fog#3011

[plribeiro3000]

cc/ @dennis-sig @geemus @krames @jclendennen @elight @rupakg @grosskop