etcd: Bump to version 3.2.6 and update all the grpc deps

Note: When go-grpc-prometheus was in the main $gopath (even at this
version) and everyone else was where they always were in vendor/ this
didn't build! It gave errors like:

	have SendHeader("github.com/purpleidea/mgmt/vendor/google.golang.org/grpc/metadata".MD) error
	want SendHeader("google.golang.org/grpc/metadata".MD) error

and I got frustrated. Putting it "next" to the other vendored deps seems
to have fixed this. Where are the golang docs that explain this
phenomenon?

This also requires golang 1.8+ as that is a requirement for etcd. It's
probably a reasonable thing for us too.

Note the older versions of etcd had some bugs with the concurrency
package and other things, so this is a necessary bump.

test/shell/file-owner.sh

@@ -9,7 +9,7 @@ if ! timeout 1s sudo -A true; then
 fi
 
 # run till completion
-timeout --kill-after=15s 10s sudo -A ./mgmt run --yaml file-owner.yaml --converged-timeout=5 --no-watch --tmp-prefix &
+timeout --kill-after=30s 25s sudo -A ./mgmt run --yaml file-owner.yaml --converged-timeout=5 --no-watch --tmp-prefix &
 pid=$!
 wait $pid	# get exit status
 e=$?