Use environment names compliant with IEEE Std 1003.1

Functions `awsenv-*` is not a valid identifier in IEEE Std 1003.1. This PR fixes this.

```
Environment variables defined in this chapter affect the operation of multiple utilities, functions, and applications. There are other environment variables that are of interest only to specific utilities.
```

See [Open Group Base Specifications - Environment Variables](http://pubs.opengroup.org/onlinepubs/000095399/basedefs/xbd_chap08.html) for more details.