Remove unnecessary client alias in AvailabilityZoneTestJson
Remove unnecessary client alias in AvailabilityZoneTestJson

The class AvailabilityZoneTestJson is inherited from base.BaseVolumeTest,
and the latter has already declared the availability_zone_client. This
patch removes the unnecessary client alias for availability_zone_client.

Change-Id: I287d742087a72928774325681bb70837ecad72f7

masayukig/tempest,masayukig/tempest,cisco-openstack/tempest,Juniper/tempest,cisco-openstack/tempest,openstack/tempest,openstack/tempest,Juniper/tempest