Add OVAL for Antivirus check

- Add OVAL for Antivirus check
- Enable for RHEL 6 & 7 and Fedora 20
[Enhancement] Update Antivirus checks

- Enable for Fedora
- Add XCCDF for Fedora
- Update RHEL 7 XCCDF for antivirus
Merge remote branch 'origin/master' into add_Antivirus_oval
Update install_antivirus.xml

Fix typo.
Update install_antivirus.xml

Use McAfee Linuxshield only to match STIG profile.
Merge pull request #30 from redhatrises/add_Antivirus_oval

Add OVAL for antivirus check