add blocking option to start/stop/restart/reload commands for server groups

In domain mode, it is possible to block when restarting individual servers, this would be a useful enhancement to add the blocking option to the start/stop/restart of server groups. This option would be useful when writing management scripts to know when the servers have complete the operation.

/host=master/server-config=example-server1:restart(blocking=true)
/host=master/server-config=example-server1:stop(blocking=true)
/host=master/server-config=example-server1:start(blocking=true)

domain mode

These would benefit from a blocking option

/:restart-servers
/:stop-servers
/:start-servers

As well as these

/server-group=main-server-group:restart-servers()
/server-group=main-server-group:stop-servers()
/server-group=main-server-group:start-servers()

standalone mode:

In standalone mode, there is shutdown with a restart option, this would also benefit from adding a blocking argument when restarting or shutting down

:shutdown(restart=true)

It looks like :reload() does not have a blocking option either, reload essentially is restarting the server, from a scripting perspective there is not a nice way to call reload then then perform some other commands, currently you have to do a sleep and then try to invoke a command catch an exception and try again later. So :reload(blocking=true) would also be useful.