snf-mkimage: export image metadata as environ vars

Export the image metadata as environment variables before running
scripts on the mounted image. This way the metadata will be visible
and can be used by the scripts if needed.

image_creator/main.py

@@ -346,6 +346,11 @@ def image_creator(options, out):
             image.os.install_virtio_drivers()
 
         if len(options.host_run) != 0:
+            # Export image metadata as environment variables to make them
+            # visible by the scripts
+            for key, value in image.meta.items():
+                os.environ["SNF_IMAGE_CREATOR_METADATA_%s" % key] = str(value)
+
             out.info("Running scripts on the input media:")
             mpoint = tempfile.mkdtemp()
             try: