The best possible criteria for deflating balloons is heap pressure: Whenever
there is pressure in the JVM, we should give back memory so pressure stops.

To accomplish that, we need to somehow tap into the JVM. This patch register
a MXBean that will send us notifications about collections. We will ignore
minor collections and act upon major collections by deflating any existing
balloons.

Signed-off-by: Glauber Costa <glommer@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>