Since commit b9753635 the task 'Ensure docker-ce is installed (Debian)' fails with an error on CentOS although it should not even run on this OS.

Prompted by: https://matrix.org/blog/2019/11/09/avoiding-unwelcome-visitors-on-private-matrix-servers

This is a bit controversial, because.. the Synapse default remains open,
while the general advice (as per the blog post) is to make it more private.

I'm not sure exactly what kind of server people set up and whether they
want to make the room directory public. Our general goal is to favor
privacy and security when running personal (family & friends) and corporate
homeservers, both of which likely benefit from having a more secure default.

Don't mention systemd-journald adjustment anymore, because
we've changed log levels to WARNING and Synapse is not chatty by default
anymore.

The "excessive log messages may get dropped on CentOS" issue no longer
applies to most users and we shouldn't bother them with it.

Removed a set_facts that I have used for tracing down the issue

matrix_synapse_storage_path is already defined in matrix-synapse/defaults/main.yml (with a default of "{{ matrix_synapse_base_path }}/storage"), but was not being used for its presumed purpose in matrix-synapse.service.j2. As a result, if matrix_synapse_storage_path was overridden (in a vars.yml), the synapse service failed to start.

Discussed in #282 (Github Issue).

Attempt at fixing #268 (Github Issue)

Fixes #255 (Github Issue).

Fixes #257 (Github Issue)