Starting with synctl lead to "no config file found"
Stopping also leads to some (code=exited, status=1/FAILURE), but at least now we can stop the service.

Non-existing files, when running the suggested from https://github.com/matrix-org/synapse#configuring-synapse
/etc/synapse/log_config.yaml so the --log-config leads to an error
/etc/sysconfig/synapse The environment-file or even the /etc/sysconfig does not exist in arch linux

Also instead of calling python2 we use synctl, as this seems to be the proper way to start it, and it gives us a more useful error in the systemctl status. And we now allow stop (and therefore restart).

merge in right archlinux package, thanks to @saram-kon from https://github.com/matrix-org/synapse/pull/1956

Now there is at least one environment variable that controls
synapse server's behaviour: SYNAPSE_CACHE_FACTOR.
So, it makes sense to make systemd unit file to use
environment configuration file that can set this variable's value.

Signed-off-by: Oleg Girko <ol@infoserver.lv>

It turned out that merely configuring the root logger is not enough for
"catch-all" semantics. The logging subsystem also needs to be told not
to disable existing loggers (so that their messages will get propagated
to handlers up the logging hierarchy, not just silently discarded).

Signed-off-by: Ivan Shapovalov <intelfx100@gmail.com>

The added logger configuration (--log-config or log_config:) uses
systemd's python bindings to pass messages directly to the journal.

Signed-off-by: Ivan Shapovalov <intelfx100@gmail.com>