sanlock: add flag SANLK_REQUEST_NEXT_LVER
    
    To cause sanlock_request() to automatically request
    the next lver so the caller does not need to specify
    the next lver, which requires reading the current one.
    This flag would produce unexpected/unwanted results
    if used by multiple hosts targetting the same owner.
    
    Signed-off-by: David Teigland <teigland@redhat.com>