tests/resource/aws_key_pair: Sweep additional EC2 key pairs
tests/resource/aws_key_pair: Sweep additional EC2 key pairs

Output from test sweeper:

```
$ aws ec2 describe-key-pairs | jq '.KeyPairs | length'
69

$ go test ./aws -v -sweep=us-west-2 -sweep-run=aws_key_pair -timeout 10h
...
2019/01/09 23:08:03 Sweeper Tests ran:
  - aws_instance
  - aws_spot_fleet_request
  - aws_key_pair
ok    github.com/terraform-providers/terraform-provider-aws/aws 58.889s

$ aws ec2 describe-key-pairs | jq '.KeyPairs | length'
5
```

Ninir/terraform-provider-aws,kjmkznr/terraform-provider-aws,kjmkznr/terraform-provider-aws,Ninir/terraform-provider-aws,Ninir/terraform-provider-aws,terraform-providers/terraform-provider-aws,kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws,Ninir/terraform-provider-aws,kjmkznr/terraform-provider-aws