NixOps should warn if deployment.ec2.associatePublicIpAddress is not set

[edolstra]

In a VPC deployment I forgot to set deployment.ec2.associatePublicIpAddress. Then NixOps will wait forever for a private IP address to become reachable:

btc....> creating EC2 instance (AMI ‘ami-d40185ad’, type ‘m5.large’, region ‘eu-west-1’)...
btc....> waiting for IP address... [pending] [pending] [running] None / 172.30.1.104
btc....> waiting for SSH..............................

[edolstra]

Also, it might be more sensible to have deployment.ec2.associatePublicIpAddress default to true.

[edolstra]

Also also, does it ever make sense in the context of NixOps to set it to false, given that NixOps must be able to connect to the instance? Maybe if you're deploying from within the same VPC, but that's probably not the most common scenario.