test/py: net: Add a test for 'pxe get' command

Execute the 'pxe get' command to download a pxe configuration file from
the TFTP server and validate its interpretation.

Signed-off-by: Love Kumar <love.kumar@amd.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
Link: https://lore.kernel.org/r/b5d263cf61282b158052ba87bde1fb4a227c0bb7.1696338593.git.love.kumar@amd.com


Signed-off-by: Michal Simek <michal.simek@amd.com>