[Build] Disable apt-cacher for Windows WSL gitian setup
[Build] Disable apt-cacher for Windows WSL gitian setup

gitian's use of apt-cacher server on the host doesn't work when using
Windows 10's WSL subsystem. This adds a check to see if the ubuntu OS
version is from "Microsoft" (which indicates it is a WSL environment),
then uses the boolean result to disable the use of apt-cacher if true.

Darknet-Crypto/Darknet,PIVX-Project/PIVX,Darknet-Crypto/Darknet,PIVX-Project/PIVX,PIVX-Project/PIVX,PIVX-Project/PIVX,Darknet-Crypto/Darknet,Darknet-Crypto/Darknet,PIVX-Project/PIVX,PIVX-Project/PIVX,Darknet-Crypto/Darknet,PIVX-Project/PIVX,Darknet-Crypto/Darknet,PIVX-Project/PIVX,PIVX-Project/PIVX