Update the private worker setup instructions

[orasimus]

Multiple updates:

• remove reference to plain Redis
• instruct to create a new Key Pair for the worker queue instance
• add valohai:1 tag to all created resources
• VPC ID should be recorded instead of VPC name
• make it clearer what needs to be recorded
• improve writing in general

[drazendee]

Looks good!

Two short notes:

• Now we're assuming we use the same SSH key for workers and queue. Which is fine, but I just wanted to mention that. In some cases, the customer will want to use a separate key to connect but that's more an exception than a rule (and it can be updated later on)
• When you add the details for the Route53 details you'll need to configure the ACME tool port 80 rule