core: GetImageInfoVDSCommand - remove apparentsize

In GetImageInfoVDSCommand appertsize is read from VDSM's response and
set in the actualSize property, just to immediately be overwritten with
truesize.
This is obviously redundant, and thus should be removed.

Change-Id: I7427258fc1d5eb9486e4296d685310c413a81214
Signed-off-by: Allon Mureinik <amureini@redhat.com>