switch ocs to struct tag based env config

ocs/pkg/logging/logging.go

@@ -0,0 +1,17 @@
+package logging
+
+import (
+	"github.com/owncloud/ocis/ocis-pkg/log"
+	"github.com/owncloud/ocis/ocs/pkg/config"
+)
+
+// LoggerFromConfig initializes a service-specific logger instance.
+func Configure(name string, cfg config.Log) log.Logger {
+	return log.NewLogger(
+		log.Name(name),
+		log.Level(cfg.Level),
+		log.Pretty(cfg.Pretty),
+		log.Color(cfg.Color),
+		log.File(cfg.File),
+	)
+}