Skip readonly controllers
Skip readonly controllers

Some system have controller directories created, but they are
read-only. Handle that case and skip optional controllers.

Closes #5887

PiperOrigin-RevId: 411907208

google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor