Add support to scan a range of IPs for the check command

[SeeRM #8737] This allows the check command to scan multiple hosts.
Fix nil rhost
Add module for CVE-2012-4554
Delete garbage comment
Add Drupal advisory as reference
Add check method
Clean code
Fix typo
Use REXML
Small fix
Ensure the rhost datastore option is restored
Be more informative about why CheckCode::Unknown

This is just kind of personal preference here. In case users wonder
why Unknown.
Land #2909 - Drupal OpenID External Entity Injection
Land #2906, check a given range