Pass MB size on copy_volume_data call copy_volume

Modify cinder/volume/driver.py method copy_volume_data
to pass size in MB when calling cinder/volume/utils/copy_volume.py

Closes-Bug #1218054

Change-Id: I5430f015ef0f0077b4794f1ff458e3f54cc4dc06
Merge "Pass MB size on copy_volume_data call copy_volume"