Install Guide: Install openstack-neutron-metadata-agent

As noted on disqus, install on openSUSE the metadata-agent as well.

Change-Id: Ied84011851343b2a1cae88ec8d0459c9d16c3eba
backport: havana
(cherry picked from commit b02b79489d5aa004826350b22e819ad872b2c74e)