arduino: allow different boards to be set from the wtfconfig

We have the mc200_dbg and gmc200_dbg boards which need to be set
depending on which one is connected.
arduino: stop ap before starting it only, and remove timeout

The timeout is handled by pxssh, which already has a 30 second timeout.
This is enough for the wifi tests.
add function for LinuxNode to start udhcpd with a generated conf

Call this function now within the arduino test to assure a dhcp lease
since the tests look for an assigned IP address.
p2p: cleanup references to iface and driver

The driver now lives inside the Iface object and is no longer an option
passed to LinuxNode.__init__() and any previous reference to iface is
changed to iface[0].name since the iface is now a list of objects.