Add libz-dev to os-svc-install to fix raring.

Before Ubuntu 13.04 libz-dev was pulled in as a dependency of the other
libraries mentioned here, but 13.04 changed the graph. Lxml and possibly
other modules link against libz during the pip install phase.

Change-Id: I201f7dd2fc40d36e5e0b193d51cfee200f946d17
Merge "Add libz-dev to os-svc-install to fix raring."