Fix hyper-v vhd real size bigger than flavor issue

In hyper-v, after deploy the image, real vhd file size will be
extended from flavor size plus vhd metadata size, this patch
fix this issue by check the vhd type and minus the vhd metadata
size according to the specific vhd type.

Fixes bug #1177927

Conflicts:
        nova/tests/test_hypervapi.py
        nova/tests/virt/hyperv/test_vhdutils.py
        nova/virt/hyperv/constants.py

Change-Id: I51223f4f778f33e73dce1e0f53e23e8d7ac77904
(cherry picked from commit 690cf0bdbe57bc05aaf013ab39e050d04a0cd9b7)
Merge "Fix hyper-v vhd real size bigger than flavor issue" into stable/grizzly