OpenBMC: restart mboxd before applying PNOR overrides
OpenBMC: restart mboxd before applying PNOR overrides

This works around the initial fix for https://github.com/openbmc/openbmc/issues/2273
" IPL: /usr/local/share/pnor/ is not cleared on PNOR updates #2273 "

Adriana says:
> the service that deletes the attr is
> obmc-flash-bios-updatesymlinks.service .. if you have access to the bmc via
> ssh, you can issue systemctl start obmc-flash-bios-updatesymlinks.service
> .. also this service is triggered when mboxd starts like
> systemctl restart mboxd.service

So, we do that just before flashing new overrides (we still call them LIDs)
and that should be safe in the case somebody has used a different method
to flash host firmware.

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