be6c35e tests: add vol-qcow2-zerocapacity test to storagevolxml2argvtest

3 files Authored by Chris J Arges 8 years ago, Committed by John Ferlan 8 years ago,
    tests: add vol-qcow2-zerocapacity test to storagevolxml2argvtest
    
    Add a testcase for the previous change to ensure zero capacity volumes can be
    defined without a backing store.
    
    Signed-off-by: Chris J Arges <chris.j.arges@canonical.com>