Update class/function name for test_extended_availability_zone.py

In test_extended_availability_zone.py, it was using class name and
function name as following:
1) ExtendedServerAttributesTest
2) assertServerAttributes

This is not accurate as this test file is for availability zone,
this patch was change the above two names to:
1) ExtendedAvailabilityZoneTest
2) assertAvailabilityZone

Change-Id: I52d6ebcb1388fc10ac92d66cae166391d46e68c1
Merge "Update class/function name for test_extended_availability_zone.py"