Support dracut domain

While trying to get a SELinux-supporting initramfs booted up (in enforcing mode, without unconfined domains) my current attempts are at dracut. But dracut itself didn't work quite well on such a system as running it in sysadm_t domain fails (some domain transitions occur which are then asked to write files in user_tmp_t which isn't allowed for those domains).

Instead of patching those domains (ldconfig_t and depmod_t) to allow writing & creating files in user_tmp_t (i.e. manage privileges) I drafted up a dracut domain (dracut_t) and grant those domains manage access to dracut_tmp_t.

To support dracut, a few changes were necessary to the policy as well (additional interfaces).

The summary:
- Add read interface for udev rules (udev_read_rules_files)
- List module configuration option files (modutils_list_module_config)
- Add in the dracut_t policy
- Grant ldconfig_t and depmod_t the dracut_manage_tmp_files privilege
- Allow sysadm_t to run/transition to dracut_t