Add the ability to run in debug mode

[ffainelli]

Hi,

Sometimes not all commands will work, so we need to be able to run in debug mode, having the ability to show which commands are being run (along with their actual arguments) on the host/board is helpful

[d-k-c]

Agreed, but using a simple print will mess with unittest output. I think using a logger would also us to print to stderr or to a file quite easily (let --debug take an argument, default to stderr if none specified). What do you think?

[ffainelli]

That seems to be a much better way to achieve that!