The sd_notify method is used to tell systemd when libvirtd
has finished starting up. All it does is send a datagram
containing the string parameter to systemd on a UNIX socket
named in the NOTIFY_SOCKET environment variable. Rather than
pulling in the systemd libraries for this, just code the
notification directly in libvirt as this is a stable ABI
from systemd's POV which explicitly allows independant
implementations:
See "Reimplementable Independently" column in the
"$NOTIFY_SOCKET Daemon Notifications" row:
https://www.freedesktop.org/wiki/Software/systemd/InterfacePortabilityAndStabilityChart/
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1314881
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>