[feature suggestion] redis-cli --wait and --wait-cluster

[dvirsky]

When I'm scripting redis setups, I want to wait until redis is ready for business (rdb loaded, replication in sync, etc). Especially in a cluster, I want to wait until the cluster state is ok.

It would be cool if instead of writing busy loops, redis-cli could automate this, and supports a mode where it waits (with timeout) until redis is ready or the cluster is okay, and then returns with 0 code if all ok, or -1 on timeout.

So my script can look like

foreman start -f Procfile.cluster & \
  redis-cli --wait-cluster 10 && \
  do_something()