Don't take an exception if the manifest doesn't exist.

- This is useful particularly for imports from the loader.

packages/base/all/vendor-config-onl/src/python/onl/versions/__init__.py

@@ -1,3 +1,4 @@
+import os
 import json
 
 class OnlVersionManifest(object):
@@ -30,8 +31,8 @@ class OnlLoaderVersion(OnlVersionBase):
 #
 # print onl.versions.rootfs.BUILD_TIMESTAMP
 #
-
-rootfs = OnlRootfsVersion()
-loader = OnlLoaderVersion()
+rootfs = OnlRootfsVersion() if os.path.exists(OnlRootfsVersion.MANIFEST) else None
+loader = OnlLoaderVersion() if os.path.exists(OnlLoaderVersion.MANIFEST) else None
+