Adds section for memcached settings in manifests

[rdoxenham]

The current manifests do not offer the user the chance to override the default memcached settings. It always defaults to the localhost. This change updates the manifests to allow the user to override.

Note that we'll need to update the installer packages to set a default override parameter.

BZ #1063372 - No option to specify memcache details for Horizon in manifests https://bugzilla.redhat.com/show_bug.cgi?id=1063372

[jguiditta]

I notice that you have not added this for nova_network/controller.pp. Is that just an oversight, or is there a reason? Also, can you rebase your branch against origin/master and then force push? There is currently a dirty git history here, and it is not merge-able as is (as we didn't have time to get to is as we were finishing up a release when you posted this).