Fixes Hyper-V agent unsopported network_type issue

Fixes an issue when an exception is raised in case of not supported
network types.

Fixes bug: #1224583

Change-Id: I847aa825fbf5b7086c9960c051014cc1d7515f62
Merge "Fixes Hyper-V agent unsopported network_type issue" into stable/grizzly
Merge branch 'stable/grizzly' of https://github.com/openstack/quantum into grizzly/stable