Fixed a bug when giving in another logging driver than syslog.

Before this commit, if the Logging config did not contain a logging option "syslog-address", it would definitely insert this option.
If then, you decide to take another logdriver than syslog, docker would fail because it received a wrong log option for the selected driver.
Now, nomad will only insert the syslog address in a hard way if there are no logging options at all - this way it keeps the default nomad settings.

client/driver/docker.go

@@ -438,9 +438,6 @@ func (d *DockerDriver) createContainer(ctx *ExecContext, task *structs.Task,
 		d.logger.Printf("[DEBUG] driver.docker: Setting default logging options to syslog and %s", syslogAddr)
 		if driverConfig.Logging[0].Type == "" {
 			driverConfig.Logging[0].Type = "syslog"
-		}
-
-		if driverConfig.Logging[0].Config["syslog-address"] == "" {
 			driverConfig.Logging[0].Config["syslog-address"] = syslogAddr
 		}
 	}