Add apparmor change hat functionality to fpm

With this patch the pool config gets the additional parameter apparmor_hat.
Workers of this pool change their app armor hat to the configured one during spawn.

Original Pull Request: #343
Changed aa_change_hat to aa_change_profile. Thx to @jjohansen for spotting the error.
RFC: https://wiki.php.net/rfc/fpm_change_hat