lock_daemon: Switch to wrapper locking functions
    
    Lets use wrapper functions virLockDaemonLock and
    virLockDaemonUnlock instead of virMutexLock and virMutexUnlock.
    This has no functional impact, but it's easier to read (at least
    for me).
    
    Signed-off-by: Michal Privoznik <mprivozn@redhat.com>