openstack-full: Use Debian meta-packages for linux-{headers,image}

Debian build is broken due to an NMU on Linux kernel,headers; This
commit update packages names, using meta-packages in order to avoid
potential future issues.

linux-headers-3.16-0.bpo.3-amd64 →  linux-headers-3.16.0-0.bpo.4-amd64
linux-image-3.16-0.bpo.3-amd64 → linux-image-3.16.0-0.bpo.4-amd64
Merge pull request #119 from enovance/debian-meta-pkg

openstack-full: Use Debian meta-packages for linux-{headers,image}