While uploading a Volume to an image, the HTTPConnection's request method does
not set the Content-Length header (since the volume file is a sym link i.e. the
os.fstat call returns a st_size of 0). This causes Volume uploads to Glance
fail (since the image data is ignored as no content-length is specified).
Therefore setting the Content-Length from update( ) method if the image data is
provided.
Fixes LP: #1045824
Change-Id: If259fc5a338e3e90214a52b773132ed901691c0f
30d8e1b97c