Corrected check to platform

A recent mistake I noticed I made when checking platform. It used to only check meterpreter for the os flavor, but now it also checks the framework db in case the hosts platform was already discovered, preventing more noise on the system.

It now also utilizes msf's means of getting the OS release meaning it can be as sneaky and compatible as possible. The extra benefit is that the sysinfo call will also update the database on the host if its active, so the module can be run again and it will know the OS without doing further digging