Prepared changelog.txt for 3.4.3 release
Prepared changelog.txt for 3.4.3 release

dsukhoroslov/hazelcast,mdogan/hazelcast,mesutcelik/hazelcast,mdogan/hazelcast,emrahkocaman/hazelcast,dbrimley/hazelcast,juanavelez/hazelcast,mdogan/hazelcast,emre-aydin/hazelcast,emre-aydin/hazelcast,Donnerbart/hazelcast,juanavelez/hazelcast,lmjacksoniii/hazelcast,tombujok/hazelcast,tkountis/hazelcast,emrahkocaman/hazelcast,mesutcelik/hazelcast,dbrimley/hazelcast,Donnerbart/hazelcast,Donnerbart/hazelcast,dsukhoroslov/hazelcast,tufangorel/hazelcast,dbrimley/hazelcast,tufangorel/hazelcast,tkountis/hazelcast,lmjacksoniii/hazelcast,tufangorel/hazelcast,mesutcelik/hazelcast,tkountis/hazelcast,emre-aydin/hazelcast,tombujok/hazelcast