Display local IP

[Darkren]

Did you run make format && make check?
Yes
Fixes #389

Works only on Linux and MacOS systems

This PR also contains all the commits from #685 . So if this gets merged, #685 may be closed for good.

Changes:

• DefaultNetworkInterface, LocalNetworkInterfaceIPs, NetworkInterfaceIPs were moved from vpn to util/netutil;
• DefaultNetworkInterface was implemented for MacOS;
• local_ip field was added to the response from `/api/visors/{pk}.

How to test this PR:

1. Run visor with hypervisor
2. Open network console in browser
3. Open visor page
4. Check response from /api/visors/{pk}. It should contain local_ip field with the corresponding value for you default network interface IP

[jdknives]

Works well on Mac.

[Senyoret1]

Worked well in my test using Linux. However, I’m not sure if it will work well with #699 and the PR it depends on. Also, quick question: if it works only in Mac and Linux, what is the expected content of the local_ip field when using Windows?

[Darkren]

Worked well in my test using Linux. However, I’m not sure if it will work well with #699 and the PR it depends on. Also, quick question: if it works only in Mac and Linux, what is the expected content of the local_ip field when using Windows?

@Senyoret1 previously it couldn't be built on Windows. but I fixed it, now it will return empty string for Win