Add Powershell target/Bash default and other fixes

This does spawn the handler, thanks!

I can't test reverse shells given my setup (only inbound connections to these systems), but for the bind shells ```handler``` is not seeing them unless I explicitly set ```RHOST``` before launching or fire up ```exploit/multi/handler``` with an appropriate ```RHOST``` on my own after the fact.    This seems like a defect but I'm not sure if it is the framework or me.  Either way, what you have here is better so I'll land it.