Fix availability-zone option miss when creates an instance

In test_availability_zone.py the availability-zone option is
used as 'availability_zone' which should be modified to
'os-availability-zone:availability_zone'.

Change-Id: I765d07b699ecb425dadccb22af834b11f52ff5b0
Closes-Bug: #1270811
Merge "Fix availability-zone option miss when creates an instance"