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: NDaniel P. Berrange <berrange@redhat.com>