feat(xo-server): add XenServers from XenStore (#4194)
feat(xo-server): add XenServers from XenStore (#4194)

XenStore can be used to pass XenServers to connect to to xo-server:

`vm-data/xen-servers` entry:

```json
[
  {
    "allowUnauthorized": true,
    "host": "xs1.company.tld",
    "label": "My XenServer",
    "password": "super%secret+password",
    "readOnly": false,
    "username": "root"
  }
]
```
lmcro/xo-web,vatesfr/xo-web,lmcro/xo-web,vatesfr/xo-web,lmcro/xo-web