Increase default file handle limits for virtlockd
    
    The assumption so far was an average of 4 disks per guest.
    But some architectures, like s390x, still often use plenty of smaller disks.
    
    To include those in the considerations an assumption of an average of 10
    disks is more reasonable.
    
    Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>