[enhancement] Add OVAL for ftp_present_banner and ftp_log_transactions

- add OVAL for ftp_present_banner and enable for RHEL 6 & 7 and Fedora 20
- add OVAL for ftp_log_transactions and enable for RHEL 6 & 7 and Fedora 20
Update ftp.xml
[Enhancement] Fedora FTP support

- Enable Fedora support
- Add missing vsftpd OVAL check
Merge pull request #24 from redhatrises/add-ftp-banners

[Enhancement] Add OVAL for ftp_present_banner and ftp_log_transactions checks