Split destinations by commas to handle comma-delimited lists

[dsabeti]

When a user of CF defines an ASG, it is usually of the form:

[
  {
    "protocol": "tcp",
    "destination": "10.0.10.0/24",
    "ports": "80,443",
    "log": true,
    "description": "Allow http and https traffic to ZoneA"
  },
 {
    "protocol": "tcp",
    "destination": "10.0.20.0/24",
    "ports": "80,443",
    "log": true,
    "description": "Allow http and https traffic to ZoneB"
  }
]

This commit will allow users to define the destinations with comma-delimited lists, allowing the previous ASG to be condensed to:

[
  {
    "protocol": "tcp",
    "destination": "10.0.10.0/24,10.0.20.0/24", 👈 🥳
    "ports": "80,443",
    "log": true,
    "description": "Allow http and https traffic to ZoneA and ZoneB"
  }
]

#186770285

[jrussett]

Looks good to me!