[RHEL/6] audit_config_immutable rule:
* Unify XCCDF ID with OVAL ID (in XCCDF & also in profile references
so the remediation call would work),
* Add RHEL-6 remediation.
Merge pull request #356 from iankko/rhel6_audit_immutable

[RHEL/6] audit_config_immutable rule - Unify XCCDF ID with OVAL ID & add remediation