RBAC - Added "viewer" to list of roles able to connect

To test in Karaf/Fabric8:

```
jaas:manage karaf
jaas:manage --realm karaf
jaas:useradd myuser myuser
jaas:roleadd myuser viewer
jaas:update
```
Merge pull request #1554 from paoloantinori/add_view_role

RBAC - Added "viewer" to list of roles able to connect