mysql/mysql55: Log to stderr instead of logfile.

This should integrate the logging more tightly into systemd, so for
example "systemctl status mysql" actually gives an overview about what's
actually going on.

This removes the logError option attribute, so in case you still want to
write into a logfile, I've introduced an option called extraOptions, so
you can use something like:

services.mysql*.extraOptions = ''
  log-error = /var/log/mysql_err.log
'';

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
postgresql: Log to stderr by default.

Now systemctl status will properly pick up the right logs.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
postgresql: Add initialScript for initial SQL.

Just like in the MySQL service module it really makes sense to provide a
way to inject SQL on the first start of the database cluster.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
postgresql: Allow to specify recoveryConfig.

This is needed for streaming replication in PostgreSQL 9.0 and higher.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>