A control jungler is one that maintains map control. Control junglers such as Shyvana are those that can easily counter-jungle, leaving the enemy jungler underleveled and underfunded. This in turn significantly decreases the potency of an enemy jungle gank.
Control junglers thus require a high degree of mobility. The ability to quickly move between camps, to be able to run to clear a ward and then return to safety quickly, and to be able to easily get in position for a countergank is important to control junglers. Shyvana, for instance, has her Burnout ability, which allows her to quickly cover large distances.
Another important aspect of a control jungler is control over map visibility. Shyvana in particular is good at this because she is innately tanky, making Oracle's Elixir a slightly less risky purchase. She also clears wards extremely quickly thanks to her Twin Bite ability.
To sum up, a control jungler exerts pressure over the enemy jungler while maintaining a map visibility advantage. A good control jungler requires mobility, fast clears, optionally a degree of tankiness, and the ability to quickly clear wards.
Just off the top of my head, I guess some examples aside from Shyvana would be Lee Sin and Udyr.