Hosts shown after disconnecting mininet when cluster is enabled

l2switch hosttracker shows hosts after disconnecting mininet when cluster feature is enabled.

Steps to reproduce:

1) Start karaf with features: odl-l2switch-switch-ui and odl-mdsal-clustering

2) Start mininet any topology, for example:
sudo mn --controller=remote,ip=127.0.0.1 --switch=ovsk,protocols=OpenFlow13 --topo tree,2

3) Do a mininet pingall and verify hosts show correctly in dlux

4) Stop mininet

5) Check there are some hosts still showing in dlux

BR/Luis