[AntEater]

This does not give you free reign in how to use force.
In fact, a geneva convention signatory is first and foremost bound herself.
No matter who the enemy is.
Non state actors were not yet in consideration in the 19th century, but even the geneva convention recognizes the forces of a "levee en masse" as combatants.
This was included especially to protect revolutionary forces.
Used as an analogy, this means that even partisans, freedom fighters, terrorists or however you wish to define irregular, non state combatants fall under the protection of the Geneva convention.
You don't get a free reign just because your enemy is not a recognized state.
The geneva convention even binds you if the enemy is a recognized state but has declined to sign the convention. The convention limits first and foremost the means of warfare of the signatory state. It is not a mutual agreement on force limitation, but rather, a one sided declaration of limited use of force.

But as previous posters said, cluster munitions are not generally outlawed in international law.
Many believe they should and many states, not including the US and Russia, have signed a treaty which is supposed to limit their use, but even there almost all signatory states left themselves legal loopholes.
Germany signed the treaty but has declared it will keep her existing cluster munitions for national defense until a new generation of cluster weapons becomes available that have a much lower dud rate.

And regarding its use on civilians, there were civilian deaths on both sides, but I suppose neither side had hurting civilians as their prime objective.
The war was simply too short for "Bomber Harris" style terror bombing.
The georgians had to overcome quite substantial defenses in the initial attack. These were in a city, hence civilian deaths from cluster munitions. The russians, despite georgian propaganda, had the main aim of dismanteling the georgian military. In a non-desert area, there's always a good chance of area weapons hitting civilians.
But sides simply had other objectives in this war, at least on command level. On the ground, I suppose both sides committed atrocities (you can't send the Vostok battalion somewhere and expect a clean war!) but these were not the primary objective.