Add a helper, `parse_config`, to parse a selinux configuration file,
see selinux(8), and return a dictionary containing the configuration
data in key, value pairs. This, in turn, can be fed into the other
helper method, `config_get_policy`, to get the effective policy or
`None` if SELinux is disabled or the policy type is not configured.
Add a new test suite that checks the basic functionality of the
helpers above.