Add missing specs for Service

[postmodern]

The following methods do not have specs:

• #ssl? (requires //service[@tunnel="ssl"])
• #protocol (requires //service[@proto])
• #extra_info (requires //service[@extrainfo])
• #hostname (requires //service[@hostname])
• #os_type (requires //service[@ostype])
• #device_type (requires //service[@devicetype])
• #fingerprint (requires //service[@servicefp])

Not all of the required data is present in the current spec/scan.xml. We may have to scan a more rich server; maybe snorby.org?