This reverts commit 8d774db3bc.

Docker is released in the Docker CE stable repository now.

Additionally, it's version 18.03, which doesn't suffer
any of the problems we've observed with 18.05 (edge/nightly).

This playbook does not set up guest access in Synapse anyway,
so until the need comes (or someone asks for it), guest access
is removed from riot-web's UI too.

As for supporting custom URLs, this is also not something
that seems like it'd be useful to most deployments.

It's not really a requirement, as it can function without it.
Also, restarting matrix-coturn doesn't need to restart matrix-synapse.

We have 2 blockers that prevent us from adding support:

- the Docker CE repository does not publish a `docker-ce` package
in the `stable` channel. It's still in `edge`
(can be worked around by using `edge`, but we'd better not)

- Docker bind propagation has troubles on Docker CE 18.05,
which breaks matrix-synapse.service from starting, as it wants to do
a `:slave` mount. See https://github.com/moby/moby/issues/37032

Since cbee084ac19b6, this playbook supports Postgres 10.x,
but keeps existing Postgres-9.x installs on 9.x.

This playbook can now also be ran with `--tags=upgrade-postgres`
to make it upgrade from Postgres 9.x to 10.x (or other versions
in the future).

This playbook just tries to avoid trying to setup a Postgres 10
database with existing 9.x files, as that makes Postgres complain.

Due to this, existing installs (still on 9.x) are detected
and left on Postgres 9.x.
They need to be upgraded to Postgres 10.x manually.

Switching from from avhost/docker-matrix (silviof/docker-matrix)
to matrixdotorg/synapse.

The avhost/docker-matrix (silviof/docker-matrix) image used to bundle
in the coturn STUN/TURN server, so as part of the move,
we're separating this to a separately-ran service
(matrix-coturn.service, powered by instrumentisto/coturn-docker-image)

A `.log.config` file may be generated with a different
level of indentation depending on which (Docker image, etc.)
generates it.

With this patch, we tolerate different levels of indentation
(2 spaces, 4 spaces, etc.) and don't break the configuration.

Improves performance of media store operations.

Silvio announced that he's no longer maintaining his images,
so we're jumping to AVENTER-UG's fork.

When using matrix-nginx-proxy, the file permissions are organized
in a way that matrix-nginx-proxy could read the challenge files
produced by acmetool.

However, when another own/external webserver was used (like nginx
with our generated sample configuration), this could not work.
From on we're proxying the HTTP requests to port :402 in such a case,
which fixes the problem.

The matrix-nginx-proxy was reloaded on the 3rd day of the month (`15 4 3 * *`),
which makes no sense - it's too infrequently.

It's in line with the renewal time now (+5 minutes).

Prevents clashes with other services like this one.

The non-working script is supposed to be fixed
by https://github.com/matrix-org/synapse/pull/2375

To have it work, we'd need an updated Docker image
of `silviof/matrix-riot-docker:latest`, which is not yet available
at the time of this commit.

Still, the previous patched synapse_port_db didn't work well either,
so it's not like we're regressing much by getting rid of it.

As described here (
https://github.com/matrix-org/synapse/issues/2438#issuecomment-327424711
), using own SSL certificates for the federation port is more fragile,
as renewing them could cause federation outages.

The recommended setup is to use the self-signed certificates generated
by Synapse.

On the 443 port (matrix-nginx-proxy) side, we still use the Let's Encrypt
certificates, which ensures API consumers work without having to trust
"our own CA".

Having done this, we also don't need to ever restart Synapse anymore,
as no new SSL certificates need to be applied there.

It's just matrix-nginx-proxy that needs to be restarted, and it doesn't
even need a full restart as an "nginx reload" does the job of swithing
to the new SSL certificates.

Moving keeps everything in the /matrix directory, so that we
wouldn't contaminate anything else on the system or risk
clashing with something else.

Also retrieving certificates separately for the Riot and Matrix domains,
which should help in multiple ways:

- allows them to be very different (completely separate base domain..)

- allows for Riot to be disabled for the playbook some time later
  and still have the code not break

Let's let the admin set them as they wish.
We don't care what they are anyway.

If other things run on the same server,
it's also better not to hijack these for our
own purposes, especially when we don't need to.

The timedatectl call also seems to fail on Ubuntu 17.04
for some reason (missing timezones information file?).