Add check and reporting to apache_mod_cgi_bash_env

And some additional improvements.

## Verification steps:

- [ ] Run the check command on ```auxiliary/scanner/http/apache_mod_cgi_bash_env.rb``` against a vulnerable setup, make sure it flags the host as vulnerable.
- [ ] Run ```auxiliary/scanner/http/apache_mod_cgi_bash_env.rb``` agains a vulnerable setup. Make sure the command executes.