Fix sort agents by status

[Lifka]

Hi team,

this PR fixes the issue wazuh/wazuh-api#111.

Before:

$ curl -u foo:bar -k "http://127.0.0.1:55000/agents?pretty&sort=status&select=id,status"
{
   "error": 0,
   "data": {
      "totalItems": 6,
      "items": [
         {
            "status": "Active",
            "version": "Wazuh v3.3.1",
            "id": "000",
            "lastKeepAlive": "9999-12-31 23:59:59"
         },
         {
            "status": "Disconnected",
            "version": "Wazuh v3.3.1",
            "id": "001",
            "lastKeepAlive": "2018-06-19 09:32:47"
         },
         {
            "status": "Never connected",
            "id": "002"
         },
         {
            "status": "Never connected",
            "id": "003"
         },
         {
            "status": "Disconnected",
            "version": "Wazuh v3.3.1",
            "id": "004",
            "lastKeepAlive": "2018-06-18 09:36:22"
         },
         {
            "status": "Never connected",
            "id": "005"
         }
      ]
   }
}

$ curl -u foo:bar -k "http://127.0.0.1:55000/agents?pretty&sort=-status&select=id,status"
{
   "error": 0,
   "data": {
      "totalItems": 6,
      "items": [
         {
            "status": "Never connected",
            "id": "002"
         },
         {
            "status": "Never connected",
            "id": "003"
         },
         {
            "status": "Disconnected",
            "version": "Wazuh v3.3.1",
            "id": "004",
            "lastKeepAlive": "2018-06-18 09:36:22"
         },
         {
            "status": "Never connected",
            "id": "005"
         },
         {
            "status": "Active",
            "version": "Wazuh v3.3.1",
            "id": "000",
            "lastKeepAlive": "9999-12-31 23:59:59"
         },
         {
            "status": "Disconnected",
            "version": "Wazuh v3.3.1",
            "id": "001",
            "lastKeepAlive": "2018-06-19 09:32:47"
         }
      ]
   }
}

Now:

$ curl -u foo:bar -k "http://127.0.0.1:55000/agents?pretty&sort=status&select=id,status"
{
   "error": 0,
   "data": {
      "totalItems": 6,
      "items": [
         {
            "status": "Active",
            "version": "Wazuh v3.3.1",
            "id": "000",
            "lastKeepAlive": "9999-12-31 23:59:59"
         },
         {
            "status": "Disconnected",
            "version": "Wazuh v3.3.1",
            "id": "001",
            "lastKeepAlive": "2018-06-19 09:32:47"
         },
         {
            "status": "Disconnected",
            "version": "Wazuh v3.3.1",
            "id": "004",
            "lastKeepAlive": "2018-06-18 09:36:22"
         },
         {
            "status": "Never connected",
            "id": "002"
         },
         {
            "status": "Never connected",
            "id": "003"
         },
         {
            "status": "Never connected",
            "id": "005"
         }
      ]
   }
}

$ curl -u foo:bar -k "http://127.0.0.1:55000/agents?pretty&sort=-status&select=id,status"
{
   "error": 0,
   "data": {
      "totalItems": 6,
      "items": [
         {
            "status": "Never connected",
            "id": "002"
         },
         {
            "status": "Never connected",
            "id": "003"
         },
         {
            "status": "Never connected",
            "id": "005"
         },
         {
            "status": "Disconnected",
            "version": "Wazuh v3.3.1",
            "id": "004",
            "lastKeepAlive": "2018-06-18 09:36:22"
         },
         {
            "status": "Disconnected",
            "version": "Wazuh v3.3.1",
            "id": "001",
            "lastKeepAlive": "2018-06-19 09:32:47"
         },
         {
            "status": "Active",
            "version": "Wazuh v3.3.1",
            "id": "000",
            "lastKeepAlive": "9999-12-31 23:59:59"
         }
      ]
   }
}

Regards!