Add multi server support

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.