MEDIUM: mworker: block reloads

MEDIUM: mworker: block reloads

When reloads arrive very often (sent by some APIs), newly forked workers
almost don't have a time to load completely and to send its READY status to
master, which allows then to stop the previous worker (launched before reload).
As a result, the number of workers increases very quickly, previous workers are
still alive and the memory consumption is very high.

To avoid such situations let's return in cli_parse_reload() reload status 0
with the text ""Another reload is still in progress", if there is still a
process with PROC_O_INIT flag in the processes list.