More proper fix for #4083 (IMO), more useful failure messages

I believe what is in rapid7/metasploit-framework#4083 is actually caused by a lack of cookies in the response, and that the login attempt should abort earlier rather than continuing to try as in rapid7/metasploit-framework#4094.  

While here, I also cleaned up the vprint_error messages for the login failure cases, which makes debugging this module much easier.

## Validation

First, ```apt-get install apache2 ; a2enmod '*header*' ; /etc/init.d/apache start; ```
 - [x] Test against an HTTP server that responds positively for the OWA 2010 URLs (```mkdir /var/www/owa; touch /var/www/owa/auth.owa```, and then with ```mod_headers```, set different header values and test:
  - [x] No cookies set
  - [x] ```Header set Set-Cookie testcookie=foo;``` # with cookies, but none of the right ones
  - [x] ```Header set Set-Cookie sessionid=;```` # has one of the necessary cookies but it is empty
  - [x] ```Header set Set-Cookie "foo=bar; path=/;sessionid=f;cadata=adfasdf;"``` # has all of the necessary cookies
 - [ ] Test valid/invalid logins against real OWA 2013
 - [ ] Test valid/invalid logins against real OWA 2010