Fix sensu check json

When creating sensu checks with sensu::check, it will create a json with:
```
root@controller:/etc/sensu/conf.d/checks# cat nova_api.json 
{
  "checks": {
    "nova_api": {
      "handlers": [
        "hipchat"
      ],
      "standalone": true,
      "interval": 60,
      "command": "PATH=$PATH:/usr/lib/nagios/plugins/ check_nova_api --auth_url http://10.0.80.148:5000/v2.0 --username admin --password keystone_admin_password_oeikoa7eiThi8 --tenant admin",
      "refresh": "60",
      "subscribers": [

      ]
    }
  }
}
```

The sensu-plugin will there fail because refresh is interpreted as string instead of an integer. The provider is missing .to_i for refresh and occurrences like it is used for interval.