fix docker network caps (#2273)

Docker releases a patch release which changed the required permissions to be able to do tun devices in containers, this caused all containers to fail in tests causing us to fail all tests. This fixes it, and adds some tools for debugging in the future.

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

integration/tailscale.go

@@ -15,7 +15,7 @@ import (
 // nolint
 type TailscaleClient interface {
 	Hostname() string
-	Shutdown() error
+	Shutdown() (string, string, error)
 	Version() string
 	Execute(
 		command []string,