Logging virtual size of the QCOW2

When we boot VM with QCOW2 which virtual size of the QCOW2 is larger than
flavor's root disk size, we cannot know virtual size in the log.

Virtual size of the QCOW2 should be logged.

Change-Id: I3ed969151525cada2208f755b0116ed0eca1bdf2
Fixes: bug #1206362
Merge "Logging virtual size of the QCOW2"