This test adds a default gateway and the configuration for Google's DNS
to the target. This will be needed if the target is to download any
files from the internet for testing (at least this is the case for
RZ/G1 using cip-core).

Also updated the README for the setup_internet test.

Signed-off-by: Patryk Mungai <patryk.mungai-ndungu.kx@renesas.com>