Fix ownership on /usr/local/bin/etcd* files

Not doing so leaves the ownership of the etcd binaries to the GCP user:

```
patrick@controller-1:~$ sudo mv etcd-v3.3.9-linux-amd64/etcd* /usr/local/bin/
patrick@controller-1:~$ ll /usr/local/bin/
total 33940
drwxr-xr-x  2 root    root        4096 Aug  8 17:25 ./
drwxr-xr-x 10 root    root        4096 Aug  6 20:34 ../
-rwxr-xr-x  1 patrick patrick 18934016 Jul 24 17:13 etcd*
-rwxr-xr-x  1 patrick patrick 15809280 Jul 24 17:13 etcdctl*
```

docs/07-bootstrapping-etcd.md

@@ -31,6 +31,7 @@ Extract and install the `etcd` server and the `etcdctl` command line utility:
 {
   tar -xvf etcd-v3.3.5-linux-amd64.tar.gz
   sudo mv etcd-v3.3.5-linux-amd64/etcd* /usr/local/bin/
+  sudo chown root:root /usr/local/bin/etcd*
 }
 ```