Fix extra metadata didn't assign into snapshot image

create_image action API accept metadata parameter to add extra
metadata into snapshot image. But the current code doesn't work
for snapshot of volume based instance. This error is because the
code use var 'props' to store extra metadatas, and the code use
same var to store root bdm metadata later, then the extra metadata
is overwritten by root bdm metadata. This patch use another var
'properties' to store root bdm metadata to avoid overwrite the
extra metadata.

Change-Id: I2224905f596690e22aa71dc6541284f005ebba9d
Closes-Bug: #1347355
Merge "Fix extra metadata didn't assign into snapshot image"