Hyper-V: Use Default Switch vSwitch by default

[laozc]

Description

Default Switch with NAT was skipped as docker-machine only looks for external vSwitches.

Related issue(s)

• Currently it requires the user to create an external vSwitch to launch the VM. In some case the provision might fail when the external DHCP does not work.

[GordonTheTurtle]

Please sign your commits following these rules:
https://github.com/moby/moby/blob/master/CONTRIBUTING.md#sign-your-work
The easiest way to do this is to amend the last commit:

$ git clone -b "use-default-switch-upstream" git@github.com:laozc/machine.git somewhere
$ cd somewhere
$ git commit --amend -s --no-edit
$ git push -f

Amending updates the existing PR. You DO NOT need to open a new one.

[tstromberg]

@afbjorklund - any chance this could be merged?

[afbjorklund]

@tstromberg : merged downstream, not sure if this project is doing any more updates (due to #4537)