test/sim: allow to simulate cfs failures

test/sim: allow to simulate cfs failures

Add simulated hardware commands for the cluster file system.

This allows to tell the regression test or simulator system that a
certain nodes calls to methods accessing the CFS should fail, i.e.,
die.
With this we can cover a situation which mainly happen during a
cluster file system update.

For now allow to define if the CFS is read-/writeable (state rw) and
if updates of the CFS (state update) should work or fail.

Add 'can read/write' assertions all over the relevant methods.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
Reviewed-by: Dominik Csapak <d.csapak@proxmox.com>
Tested-by: Dominik Csapak <d.csapak@proxmox.com>