add meta-data-v2 vm_extension for worker VMs

[markdboyd]

Changes proposed in this pull request:

Add the meta-data-v2 vm_extension to the worker and iaas-worker VMs.

Notably, the meta-data-v2 VM extension sets http_put_response_hop_limit: 2, which is officially recommended by when using containers on a VM:

In a container environment, set the hop limit to 2
The AWS SDKs use IMDSv2 calls by default. If the IMDSv2 call receives no response, the SDK retries the call and, if still unsuccessful, uses IMDSv1. This can result in a delay, especially in a container environment. In a container environment, if the hop limit is 1, the IMDSv2 response does not return because going to the container is considered an additional network hop. To avoid the process of falling back to IMDSv1 and the resultant delay, in a container environment we recommend that you set the hop limit to 2. For more information, see Configure the Instance Metadata Service options.

We currently have http_put_response_hop_limit: 1 on the Concourse worker VMs and we think that it may be the source of slowness with BOSH downloading blobs from S3. This issue gives us a clue that http_put_response_hop_limit: 1 can cause general slowness when running containers on VMs: aws/aws-sdk-go#2972

security considerations

The meta-data-v2 VM extension also sets http_tokens: required which requires the use of the Instance Metadata Service v2