runners: Add new common -i/--dev-id command-line option

In an effort to standardize the way that a particular debugger or device
instance is identified when there are multiple present, introduce a new
-i/--dev-id option common to all runners that allows the user to specify
which device to interact with when there are multiple connected.

Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>