This patch adds a test to create a new volume from source.
We also include code changes to pass the right size i.e. either
size passed by the user via --size argument or the source volume
size. This case is already handled at the API layer[1] but it
helps being consistent with passing the right size value as in case
of creating a volume from snapshot or backup.
[1] 7c1a5ce7b1/cinder/api/v3/volumes.py (L381-L382)
Change-Id: Idc71636dad6bb678fe24f19b0836d2e9bd92d7d2
4710cbeca6