Solaris compatibility and "root" user compatibility

This PR adds 2 improvements:

- Adds compatibility for Solaris (local users' homes are stored in `/export/home`)
- Considers the default path for "root" account is different than regular users. Previously, if the home dir was not specified, this module would have set the home dir to "`/home/root`" which is wrong and can break things. But now it sets it to "`/root`" (Linux, etc) or "`/`" (Solaris).

Let me know what you think!