Amywinpefix-updated winpe build for R2 & VMXNET3 drivers

Added support for ADK 8.1 so that WinR2 can be supported.
Fixed extraneous comments.
Added support for loading VMXNET3 drivers in WinPE,
boot.wim, and install.wim.
Creates & exports bootmgr.exe to be used for Win R2 repo.