classes/sanity: enhance the network connectivity test
Switch to use the checkstatus fetcher API for the network connectivity test,
this has several advantages:
* we no longer print any messages to the console whilst the check is
being run
* we don't actually download anything, removing the need for tidy up and
making the code more concise
Signed-off-by: Joshua Lock <josh@linux.intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
