cmd/tailscale,ipn: minor fixes to tailscale lock commands

* Fix broken add/remove key commands
 * Make lock status display whether the node is signed

Signed-off-by: Tom DNetto <tom@tailscale.com>

tka/tka.go

@@ -705,3 +705,12 @@ func (a *Authority) KeyTrusted(keyID tkatype.KeyID) bool {
 	_, err := a.state.GetKey(keyID)
 	return err == nil
 }
+
+// Keys returns the set of keys trusted by the tailnet key authority.
+func (a *Authority) Keys() []Key {
+	out := make([]Key, len(a.state.Keys))
+	for i := range a.state.Keys {
+		out[i] = a.state.Keys[i].Clone()
+	}
+	return out
+}