Revert changes for admin server IP detection

The changes to derive the admin server IP from the DHCP server information in the Win32_NetworkAdapterConfiguration object don't seem to work reliably when the windows nodes have more than one Network Card and the admin network is not connected to the first of those cards. This simply reverts those commits and goes back to setting in statically during build time.

Should fix: https://bugzilla.novell.com/show_bug.cgi?id=866797
Thanks, I submitted https://github.com/cloudbase/adk-tools/pull/8 so it's easier for someone to try this code.