internal logging & vbox sendkeys command

Hi Patrick,

here as requested the pull request. There are a few more changes. Apart from the internal logging
I added a *sendkeys* command to the vbox provider that exposes the *console_type* 
method to the cli. I find it quite handy for testing the *:boot_cmd_sequence* for new machine
definitions. I also added special key shortcuts ```<VT1>..<VT12>```  that can be used for switching the virtual terminal (using the scancodes for Alt+F1..Alt+F12).

Cheers,
Ruben


P.S.: Have a nice weekend ;)