Change compute-hyperv driver to use fields.VMMode object
Change compute-hyperv driver to use fields.VMMode object

Nova continues to transition to using objects. vm_mode module was
moved into a object by change: I372266b158667683cad973f20976619c34538491
hv_type module was moved into a object by change:
I760737578e1f4a7b35f97b4df72cde597ac519f0

This patch modifies compute-hyperv appropriately.

Change-Id: I15d24a879172306c3560f2a21bea6a0771b508f6

stackforge/compute-hyperv,openstack/compute-hyperv,openstack/compute-hyperv