Updated IPTables OVAL

- Aligned XCCDF/OVAL namings
- Updated test/obj names within set_iptables_default_rule
- Created new OVAL set_iptables_default_rule_forward, updated XCCDF to use

make content ; make validate
Added remediation for IPTables default_rule, default_rule_forward
New OVAL for set_ip6tables_default_rule

- Created OVAL for set_ip6tables_default_rule.xml
- Created bash remediation
- Updated XCCDF to use OVAL
Fix filetype for set_iptables_default_rule_forward.sh
Merge pull request #25 from shawndwells/iptables-cleanup

IPTables section cleanup