Ensure nova-common is installed before ceilometer

Ceilometer depends on the nova user and group being
present. This change adds a dependency to nova-common
to ensure that packging will handle the user before
the ceilometer compute agent tries to add user ceilometer
to the nova group.

Fixes bug 1350980

Change-Id: Iaf950c4a487b4b25c9053d59cab4fa45a1f7390b