Minor cleanup sqlmap, description and File tests

## Verification

  - [x] Run `auxiliary/scanner/http/sqlmap.rb` under normal conditions. It need not be successful.
  - [x] Run the module after chowning or chmoding `sqlmap.py` to be not readable. See the failure message.
  - [x] Run the module after chowning or chmoding `sqlmap.py` to be not executable. See the failure message.

Happened to be looking at this module and spotted these problems.