Ensure logstash-agent serivice file with Kibana 3 startup

Add web parameter usage for multi install mode (agent)
Fix missed heap_size=512m (default 256m)

Change-Id: I6cd3748e96429db470fe25a3d727578f1a51be87
Signed-off-by: Bogdan Dobrelya <bdobrelia@mirantis.com>