Updated apt dependency to 2.3.8 to match openstack-common dependency

This was merged without bumping the Berksfile here, so it breaks to Vagrant run.
https://github.com/stackforge/cookbook-openstack-common/blob/master/metadata.rb#L18

Change-Id: Idfd0e9f6d0d8c06b3889f397267d1553f5fa1e77