OpTestPNOR: Check if PAYLOAD is marked READONLY
OpTestPNOR: Check if PAYLOAD is marked READONLY

We should fail to write to the PAYLOAD partition if it's marked
read-only.

This is a bit of a work-in-progress modification based on fixes
going into the mboxd on OpenBMC (the only mboxd that currently
enforces read-only).

Signed-off-by: Stewart Smith <ec31ab75ddf977353c8f660f92ea8b23f64aef25@linux.vnet.ibm.com>

open-power/op-test-framework,open-power/op-test-framework,open-power/op-test-framework