Results 3 issues of opt-m

support random node to perform cluster slots when node manager is initializing

fix https://github.com/alibaba/RedisShake/issues/429

FT.DROPINDEX index DD will delete key as well,but i found this delete process use del instead of unlink which cause redis block。 ``` DocTable *dt = &sp->docs; DOCTABLE_FOREACH(dt, Redis_DeleteKeyC(ctx, dmd->keyPtr));...

feature
stale