Update exploit checks

Progress group 1: Making sure these checks comply with the new
guidelines. Please read: "How to write a check() method" found in
the wiki.
Saving progress

Progress group 2: Making sure these checks comply with the new
guidelines. Please read: "How to write a check() method" found in
the wiki.
Saving progress

Progress group 3: Making sure these checks comply with the new
guidelines. Please read: "How to write a check() method" found in
the wiki.
Saving progress

Progress group 4: Making sure these checks comply with the new
guidelines. Please read: "How to write a check() method" found in
the wiki.
Saving progress
Progress
Oops, I broke this module
Add routine to check bad check codes
Update rspec for ms08_067 check

The original version doesn't return a check if the host is invalid,
looks like it was forgotten. The new version will return Unknown
instead.
Throw Unknown if connection times out
Address nil
Change check code
Remove to_s inside #{}
Update some checks
Land #2905, @wchen-r7's update of exploit checks