Update environment variables.
Update environment variables.

When running salt as a user which is not root, I've found out that, at
least pygit2, misbehaves.

Salt correctly changes to the desired user, but the environment is the
same as the root user. `libgit2` takes advantage of environment
variables to load `.gitconfig` and because the environ is kept as the
root user, it fails to load it.

```
[ERROR   ] Exception caught while initializing gitfs remote /var/cache/salt/master/gitfs/e3971c3f4ffa91eb057d362f6bfb3683: Error stat'ing config file '/root/.gitconfig': /var/cache/salt/master/gitfs/e3971c3f4ffa91eb057d362f6bfb3683: Error stat'ing config file '/root/.gitconfig'
```

saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt