[CFN HUP] - [BUG] - Environment Variables Exceeding Maximum Allowed Size for OS

### Name of the resource

Other

### Resource Name

CFN Hup

### Issue Description

While using CFN Hup, two environment variables are populated, `CFN_OLD_METADATA` and `CFN_NEW_METADATA`, which are expected to contain the entire path storing the metadata. However, an OS has a max allowed environment variable size.

If the value of the environment variable exceeds the limits of the OS, the command would fail.

### Expected Behavior

CFN Hup should automatically trim the environment variable to avoid OS related errors, or workaround this issue in a way to support CFN Hup functionality while respecting the OS limitations.

### Observed Behavior

CFN Hup currently does not automatically trim the environment variables, in which an error is observed:
```
OSError: [Errno 7] Argument list too long: 'su'
```

### Test Cases

NA

### Other Details

So far, this issue is only observed from the way cfn-hup invokes cfn-init after a stack update, implying this issue is within cfn-hup.

**To workaround this, a user encountering this issue would need to avoid cfn hup by directly calling cfn-init which would not have the environment variables set. This workaround is not ideal due to missing the functionalities provided by CFN Hup.**

Start by tracing how cfn-hup invokes cfn-init and passes CFN_OLD_METADATA and CFN_NEW_METADATA. Reproduce the oversized environment failure across the affected OS limits, then define a solution that preserves CFN Hup functionality without producing the OSError: [Errno 7] failure.

Written by the indexing model from the issue text.