Add apt-get autoremove
Add apt-get autoremove

We end up with some unneeded packages by default, we should autoremove
them before were done.

Change-Id: Ib9e08e623d952ea3c04c764511dc860915d0abb2

CSC-IT-Center-for-Science/diskimage-builder,zioproto/diskimage-builder,switch-ch/diskimage-builder,takahashinobuyuki/diskimage-builder,rdo-management/diskimage-builder,rdo-management/diskimage-builder,NaohiroTamura/diskimage-builder,openstack/diskimage-builder,zioproto/diskimage-builder,switch-ch/diskimage-builder,CSC-IT-Center-for-Science/diskimage-builder,openstack/diskimage-builder,takahashinobuyuki/diskimage-builder,NaohiroTamura/diskimage-builder