add source install option

Install `etcd` and `etcdctl` from git source. 

Made attributes for most things so an alternative git repo can be used. 

Go 1.1+ is required to build `etcd` so elected to download these as binaries.

Also changed the warning on 'install method not supported' to `fatal` as the run will abort soon afterwards due to the service not being able to be created when `etcd` isn't installed.