CLOUDSTACK-3865: Additional debug logging for size mismatch

Signed-off-by: Prasanna Santhanam <tsp@apache.org>
CLOUDSTACK-2921: Fix the change service offering test on stoppedvm

There is no need to attach a volume to the VM when doing the
changeserviceOffering test. Condensed the test to verify that the VM's
offering is changed successfully when stopped and reflects when VM is
started.

Signed-off-by: Prasanna Santhanam <tsp@apache.org>