rosmongolog_mp: init subscriber, long queue logging
rosmongolog_mp: init subscriber, long queue logging

+ Initialize subscriber to None to avoid spurious problems
+ Fixed long queue logging, was expecting "too long queues"

nilsbore/mongodb_store,jeansebbaklouti/mongodb_store,sevenbitbyte/mongodb_store,jeansebbaklouti/mongodb_store,Jailander/mongodb_store,hawesie/mongodb_store,hawesie/mongodb_store,cburbridge/mongodb_store,cburbridge/mongodb_store,nilsbore/mongodb_store,Jailander/mongodb_store,strands-project/mongodb_store,sevenbitbyte/mongodb_store,strands-project/mongodb_store