Increase size to 20GB, needed for federation database and media.

Setting `reverse_proxy_proxy_protocol: true` and
`nginx_proxy_protocol: true` in nginx roles enable the forwarding of
the original connection address from the reverse_proxy to the target
nginx instance, using the established TCP PROXY PROTOCOL (adding a TCP
header, so working also for TLS connections that are not terminated at
the reverse proxy).

**Warning**

The `reverse_proxy_proxy_protocol` settings acts globally on the
reverse proxy nodes, so every virtual server on the reverse proxy must
accept and correctly handle proxy protocol headers.

This settings must be the same for every host sharing the same reverse
proxy, otherwise the setting will be changed globally at every run.

commont task to create lxc vm in separete file `prepare_lxc_host`,
avoid redundancy of statements in each vm-specific playbook file.

Playbooks updated to import `prepare_lxc_host`:
- ldap
- matrix
- nextcloud
- projects
- status

Add role prefix to role specifig variable to avoid conflicts when
using multiples role on the same machine on the same play.

`lxc-ssh.py` removed.

All Playbbooks now user `ssh_lxc` connection.

`ansible_ssh_lxc_name` variable used to specify container name.

Tested and worked correctly with `python==3.8.2` and `ansible==2.9.6` on the
controller and `python==2.7` on the target.