MINOR: mworker/cli: indicate in the master prompt when a reload failed

MINOR: mworker/cli: indicate in the master prompt when a reload failed

If a reload was issued to the master process and failed, it is critical
that the admin sees it because it means that the saved configuration
does not work anymore and might not be usable after a full restart. For
this reason in this case we modify the "master" prompt to explicitly
indicate that a reload failed.