conf: don't iterate over backcompat console in virDomainChrDefForeach
    
    If the first console is just a copy of the first serial device we
    don't need to iterate over the same device twice in order to perform
    actions like security labeling, cgroup configuring, etc.
    
    Currently only security SELinux manager was aware of this fact.
    
    Signed-off-by: Pavel Hrdina <phrdina@redhat.com>