Add Exchange 2007 POP3 Quit Message banner pattern

[cfleming-R7]

Description

Add a banner pattern for a quit message for Microsoft Exchange Server 2007

Motivation and Context

We observed a POP3 quit message exposing the underlying service, in this case Microsoft Exchange Server 2007. A pattern has been added to match against that banner

How Has This Been Tested?

• rake tests
• bundle exec ./bin/recog_verify xml/pop_banners.xml

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist:

• [x] I have added tests to cover my changes (or new tests are not required).
• [x] All new and existing tests passed.

[mkienow-r7]

I don't believe xml/pop_banners.xml is the correct place for quit messages since that is not really the banner. For "SMTP response lines to the QUIT command" we have xml/smtp_quit.xml so this would belong in a new database xml/pop_quit.xml.