feat(builder) replace boot with go and add use the data store to reuse ssh keys

This introduces the use of deis-store to backup and restore the ssh configuration of the builder so if the deis-builder is scheduled in other host the ssh keys will be the same.

*Running output:*
```console
$ docker run --rm -p 2223:22 --volumes-from=deis-builder-data -e EXTERNAL_PORT=2223 -e HOST=$COREOS_PRIVATE_IPV4 --privileged <image>
waiting for missing etcd keys...
waiting for missing etcd keys...
restoring SSH keys from the store...
loading cedarish...
building slugbuilder and slugrunner...
Server listening on 0.0.0.0 port 22.
Server listening on :: port 22.
deis-builder running...
```

To provide more info the app use go-debug to use `-e DEBUG=*` and get more information

```console
$ docker run --rm -p 2223:22 --volumes-from=deis-builder-data -e EXTERNAL_PORT=2223 -e HOST=$COREOS_PRIVATE_IPV4 --privileged <image>
03:40:38.656 6us    5us    builder:boot - Starting deis-builder...
03:40:38.660 3ms    3ms    builder:boot - returning default value "4001" for key "ETCD_PORT"
03:40:38.660 3us    3us    builder:boot - returning default value "/deis/builder" for key "ETCD_PATH"
03:40:38.660 3us    3us    builder:boot - returning default value "btrfs" for key "STORAGE_DRIVER"
waiting for missing etcd keys...
waiting for missing etcd keys...
03:40:50.684 12s    12s    builder:store - Connecting to the store deis-store.local.deisapp.com (fake name)
03:40:50.684 104us  104us  builder:store - connecting to ceph store
03:40:50.941 256ms  256ms  builder:store - checking if there is a backup of the ssh files in the store
restoring SSH keys from the store...
2014/10/21 03:40:51 105: Key already exists (/deis/builder/users) [26577]
03:40:51.483 12s    12s    builder:boot - Waiting for docker daemon to be available...
03:40:51.485 2ms    2ms    builder:boot - starting docker daemon...
03:40:52.752 1s     1s     builder:boot - checking for cedarish...
loading cedarish...
building slugbuilder and slugrunner...
03:42:16.323 83s    83s    builder:boot - building image deis/slugbuilder...
03:45:37.262 200s   200s   builder:boot - building image deis/slugrunner...
03:48:13.535 156s   156s   builder:boot - starting ssh server...
Server listening on 0.0.0.0 port 22.
03:48:13.717 181ms  181ms  builder:boot - docker daemon started...
Server listening on :: port 22.
deis-builder running...
```

After the first run:

```console
$ docker run --rm -p 2223:22 --volumes-from=deis-builder-data -e EXTERNAL_PORT=2223 -e HOST=$COREOS_PRIVATE_IPV4 --privileged <image>
waiting for missing etcd keys...
waiting for missing etcd keys...
restoring SSH keys from the store...
2014/10/21 03:49:01 105: Key already exists (/deis/builder/users) [30103]
cedarish already loaded
building slugbuilder and slugrunner...
Server listening on 0.0.0.0 port 22.
deis-builder running...
Server listening on :: port 22.
```

this requires #2131