cluster/node events (#1855)

[NaughtySora]

Description

Adding events for cluster client, some people were interested in it.
I have read the issue but didn't see any concrete approved suggestions so i come up with some.

for cluster:

1. connect - when cluster ready.
2. disconnect - when cluster is closed.
3. error (already exists).

for nodes:

1. node-connect - when tcp socket connected.
2. node-ready - when tcp socket are ready.
3. node-reconnecting - when tcp socket is reconnecting.
4. node-disconnect - when tcp socket disconnected.
5. node-error - when tcp socket errored.

Node events provide host/port to identify a particular node.

I would like to hear suggestions or opinion if this feature needed.

issue #1855

Checklist

• Does npm test pass with this change (including linting)?
  I tried to run tests via npm run build and npm test but it fails with timeout "before hook" after 30000ms after 1 hour of going a couple of time. But git checks are fine i guess.

• Is the new or changed code fully tested?
  I haven't seen any tests for emitting events, i have tested it only locally.

• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?
  Can't find where i can update desctiption about cluster events.
  I saw small section of client events on redis website.
  Can't update that.