- Move the qemu config to a common file shared by qemu and qemu4.
- Disable nettle on qemu4, FreeBSd complained.
- Add some extra git cleaning steps to the git path. These however
do not full clean the qemu submodules and it is not worth the
effort to try and fix.
- The devel/qemu will not build on machines with python set to
python3. This will not be fixed, use qemu4.
Closes#3966
