c6eea54 storage: allow zero capacity with non-backing file to be created

1 file Authored by Chris J Arges 8 years ago, Committed by John Ferlan 8 years ago,
    storage: allow zero capacity with non-backing file to be created
    
    In commit 155ca616e, a change was introduced that no longer allowed defining
    volumes via XML with a capacity of '0'. Because we check for info.size_arg
    to be non-zero, this use-case fails. This patch allows info.size_arg to be
    zero if no backing store is specified.
    
    Signed-off-by: Chris J Arges <chris.j.arges@canonical.com>