Hyper-V: Use Default Switch vSwitch by default

[laozc]

This PR uses Default Switch as a fallback if the specified target is not found or not specified.

[afbjorklund]

Please open a PR upstream (https://github.com/docker/machine) as well, thanks.

[afbjorklund]

Thanks, docker#4732

[blueelvis]

Thanks for the contribution :) . Please look at the review comments.

[blueelvis]

@afbjorklund - Can we merge this once the comments are addressed? I will then change our package source to this for Hyper-V. Sounds good?

[blueelvis]

@laozc - The changes look good!

@afbjorklund - This looks good. Please merge it.

@tstromberg - If this is merged, should I switch the packages to point to this repository instead? We need to get testing infra working for this as well if we are to move to this repository going forward...

[tstromberg]

@blueelvis - Yes, we should update minikube's dependency pinning to make use of this feature. It's a huge win for users.

For minikube, I'm happy to test this ad-hoc for now while we work out the reliability issues around our Hyper-V machines (tests are now active but only succeed once per reboot). If you are asking about hooking the machine-drivers testing infrastructure to our machines, that isn't currently planned and would require some discussion.

[blueelvis]

@afbjorklund @tstromberg - Please merge this PR into the repo and I will configure our repository to use this instead of the main machine repo.

Regarding testing infrastructure, can't we have at least somewhat temporary mechanism to do it via Travis?

[tstromberg]

@blueelvis - Yes, getting Travis support for this repository would be entirely reasonable.

[gbraad]

The switch should be identified by the ID and not using any string, else the Switch will not be located on localized platforms.

[gbraad]

In older versions of Windows 10 the name Default Switch is localized and it will only properly work when the ID is used to get the switch. This ID never changes.

	hypervDefaultVirtualSwitchName = "Default Switch"
	hypervDefaultVirtualSwitchId   = "c08cb7b8-9b3c-408e-8e30-5e16a3aeb444"

When the localization issue got resolved I can't remember, but for fallback in Minishift and CRC we keep using the ID to get the vSwitch.

[afbjorklund]

Getting some mixed messages here, should it be merged or does it need further additions ?

As far as I know this repository doesn't even do releases, so I'm not sure if it will do checks ?

[tstromberg]

@laozc - Thanks for the update! It looks good, but would like @gbraad to give his blessing.

[gbraad]

I would suggest to merge this, but add modifications when the mention issues show up. We have made a strong cut-off for CRC (the successor to Minishift) so we prevent this issue. But since Minikube does not have any version checks, you might end up people trying this on the Fall Creator's update and unable to select the correct virtual switch.