Fix an endianess issue in pymeterpreter registry_query_value.

This PR addresses an endianess issue in the registry query value function.  DWORD values need to be changed to big endian apparently.

```
msf4-git (S:2 J:1)  post(registry) > sessions -i 1
[*] Starting interaction with 1...

meterpreter > sysinfo
Computer     : ERMAHGERD
OS           : Windows 7 6.1.7601
Architecture : x86_64
Meterpreter  : python/python
meterpreter > background 
[*] Backgrounding session 1...
msf4-git (S:2 J:1)  post(registry) > set SESSION 1
SESSION => 1
msf4-git (S:2 J:1)  post(registry) > run

[*] Running against session 1
[*] Session type is meterpreter and platform is python/python
[*] PENDING: should evaluate key existence
[*] PENDING: should evaluate value existence
[+] should read values
[+] should return normalized values
[+] should enumerate keys and values
[+] should create keys
[+] should write REG_SZ values
[+] should write REG_DWORD values
[+] should delete keys
[*] Testing complete in 2.915975545
[*] Passed: 7; Failed: 0
[*] Post module execution completed
msf4-git (S:2 J:1)  post(registry) > 
```