hyperv: Map Limit to max_memory and VirtualQuantity to cur_balloon

hyperv: Map Limit to max_memory and VirtualQuantity to cur_balloon

Hyper-V uses its own specific memory management so no mapping is going to
be perfect. However, it is more correct to map Limit to max_memory (it
really is the upper limit of what the VM may potentially use) and keep
cur_balloon equal to total_memory.

The typical value returned from Hyper-V in Limit is 1 TiB, which is not
really going to work if interpreted as "startup memory" to be ballooned
away later.

Signed-off-by: Ladi Prosek <lprosek@redhat.com>