Make Windows Build Machine from public URLs (step 3)

This is the last of 3 set of changes to be able to install all tools needed to setup a Windows build machine.

Changes to achieve this are:

Put  8.0 signtool in the path
Install  WinDDK 7.1 from public ISO
Install 7zip and download WinDDK 7.1 public ISO
Allow Win8SDK to download sdksetup.exe
Use public URL for SDKWin8
Change WDKWin8 URL into two public URLs
Delete install-msms.ps1
Make install-wdk-win8.ps1 download exe and msi
Remove MSM URL and step (this requires change in msi-installer repo, pull request already sent)
This looks a bit suspicious but other than that, the rest looks good. Provisional ACK