[Reviewer: Mike] Memcached GR fixes

Mike,

Please can you review my fixes to memached?  These were made to support your testing earlier this week and has been tested both spinning up GR and non-GR deployments.

The key change is to the memcached remote_cluster_settings file - previously it contained local IP addresses from the other deployment (which obviously weren't routable) - now it contains public IP addresses.

There is also a change to always include the stats package on sipp nodes - this isn't really related, but is useful (and otherwise harmless).

Matt