logging: add client for virtlogd daemon
    
    Add the virLogManager API which allows for communication with
    the virtlogd daemon to RPC program. This provides the client
    side API to open log files for guest domains.
    
    The virtlogd daemon is setup to auto-spawn on first use when
    running unprivileged. For privileged usage, systemd socket
    activation is used instead.
    
    Signed-off-by: Daniel P. Berrange <berrange@redhat.com>