Improve UX by accepting different mac address formats

[andreamtp]

The tool require the mac address to use ":" as divider, but in the BMC UI can be found expressed with - as well.
In PR #5 I've added a missing example in the web gui to help avoiding user frustration, at the same time would be nice
if the program would address this, but substituting in backend the divider specificed as aa-bb-cc-... into aa:bb:cc:... .