Provide `coordinators FORCE` in fdbcli

I've run into a situation where I wanted to change the coordinators after some host failures, but the ending coordinator configuration I'd like the cluster to be in includes one of the currently failed hosts. In such a case, `coordinators` will return with a warning that not all coordinators are reachable and not do the coordination change. There's no way to force the coordinator change regardless, it'd be nice to have a `coordinators force +` so that I don't have to wait until the host is back up to issue the coordinator changes.