Revert "build: Do not depend on python while creating the relative path"

This patch while it fixes a few bugs, introduces other issues, espcially
when building on windows.

This reverts commit ae327c60.

Change-Id: I1ffcd6c88d17f5bd6a66df28d99d2d27c0683930
Signed-off-by: Anas Nashif <anas.nashif@intel.com>