Fix: disable ExecPreStart check

- doesn't seem to be able to get the env vars on CentOS7
 - seems like a known problem

templates/minio.service.j2

@@ -20,7 +20,7 @@ Group={{ minio_group }}
 PermissionsStartOnly=true
 
 EnvironmentFile={{ minio_server_envfile }}
-ExecStartPre=/bin/bash -c "[ -n \"${MINIO_VOLUMES}\" ] || echo \"Variable MINIO_VOLUMES not set in {{ minio_server_envfile }}\""
+#ExecStartPre=/bin/bash -c "[ -n \"${MINIO_VOLUMES}\" ] || echo \"Variable MINIO_VOLUMES not set in {{ minio_server_envfile }}\""
 
 ExecStart={{ minio_server_bin }} server $MINIO_OPTS $MINIO_VOLUMES