Add multi server support

[radilr1]

This pull request includes the fixes from the previous pull requests and they should be merged first.
To enable load balancer in the node add the following lines:

    "private_ip": "192.168.1.10",                         // if the server is used as slave by loadbalancer or postgre
    "nginx": {
      "load_balancer": ["192.168.1.10", "192.168.1.11"],  //install the load balancer in nginx
      "load_balanced": true                               // if the server is load balanced
    },

To enable the postgres replication add:

    "postgresql": {
      "nodes": ["10.128.180.129", "10.128.181.7"],
      "replication": "slave"
    },

Note: the database.host should point to the master server.