Package etcd version 0.4.6

Package etcd, a highly-available key value store for shared configuration
and service discovery. I'm planning to use this in conjuction with
locksmith to coordinate automatic reboots:

https://github.com/coreos/locksmith

This build is for Trusty, but since it's a Go binary with almost no
dependencies, we can use the same binary for Precise.
Merge pull request #73 from alphagov/73607174-etcd

[#73607174] Package etcd version 0.4.6