DNS: Windows Server 2008 SP2, performance and other coverage tweaks

[tsellers-r7]

Description

This PR adds coverage for an additional DNS fingerprint of DNS running on Microsoft Windows 2008 SP2. There are other misc DNS tweaks as well and some performance related changes.

The main thing I'm concerned about is the 'assert nothing' results that end up assigning a service.protocol value which is inherited from the XML database.

$ echo '' | bin/recog_match xml/dns_versionbind.xml 

MATCH: {
  "matched"=>"empty string -- assert nothing.", 
  "service.protocol"=>"dns", 
  "fingerprint_db"=>"dns.versionbind", 
  "data"=>""}

I'm addressing this by setting service.certainty to `0.0. It this logic makes sense we can apply it elsewhere when the same assert nothing style matches are used.

$ echo '' | bin/recog_match xml/dns_versionbind.xml 

MATCH: {
  "matched"=>"empty string -- assert nothing.", 
  "service.certainty"=>"0.0", 
  "service.protocol"=>"dns",
  "fingerprint_db"=>"dns.versionbind", 
  "data"=>""}

Motivation and Context

Coverage

How Has This Been Tested?

rspec, local testing

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have updated the documentation accordingly (or changes are not required).
• I have added tests to cover my changes (or new tests are not required).
• All new and existing tests passed.