Update Exploit Checks and a msftidy to go with it

This PR updates all existing checks found in exploits to follow the new guidelines:
https://github.com/rapid7/metasploit-framework/wiki/How-to-write-a-check()-method

Before you actually decide to merge this PR, make sure #2894 is merged first. That one updates the API documentation about how check codes are used.

## Verification Steps:

Obviously there's a lot of files, will take time to review. Make sure to do:

- [x] Run msfconsole, and make sure no modules are broken.
- [x] Run msftidy and look for bad check codes, like so: ```tools/msftidy.rb modules/exploits/ |grep checkcode```