[#46491831]
The root element was web_page in the source for example that tests that
import_msf_web_vuln_element creates an Mdm::WebVuln. The root element
name did not actually matter for the example, but it looked like an
error and was confusing to read the setup that root element was web_page
instead of the correct web_vuln.
[#46491831]
Move Msf::DBManager#import_msf_xml into
Msf::DBManager::ImportMsfXml#import_msf_xml and include
Msf::DBManager::ImportMsfXml to cut down size of the infamous db.rb.
Break up #import_msf_xml to have separate methods for parsing web_forms,
web_pages, and web_vulns. The method for
web_vulns, #import_msf_web_vuln_element is needed so that it can be overridden in
Pro to handle the Pro-only changes to Mdm::WebVuln.