Fix VMware Hyper can't honor hw_vif_model image property.

Support setting instance vif model through image property,
change default vif model to e1000. Available vif model options
for VMware Hyperv is "VirtualE1000, VirtualPCNet32, VirtualVmxnet".

DocImpact
Fix bug #1183192

Change-Id: I3a98bc26df7e2252bf043a71acbba2a158e213b8
Merge "Fix VMware Hyper can't honor hw_vif_model image property."