runner: Bump network ping deadline to 40 seconds

Commit ddfde25f ("runner: Add support for aborting on
network failure") introduced a 20 second deadline for the DUTs
network to recover after a suspend/resume cycle. If the network
isn't back up within that time, igt_runner aborts the test run
to save logs and prevent potential log loss from an imminent
power cycle.

External monitoring machine checks DUTs health and if it cannot
reach it over network for 60 seconds it will reboot DUT.

Although our CI system can be configured with a longer wait
time, extending it further would unnecessarily prolong tests in
cases of DUT hangs.

Bump the deadline to 40 seconds to prevent a premature igt_runner
abort.

Cc: Katarzyna Piecielska <katarzyna.piecielska@intel.com>
Cc: Ewelina Musial <ewelina.musial@intel.com>
Cc: Mateusz Grabski <mateusz.grabski@intel.com>
Cc: Konrad Brodzik <konrad.b.brodzik@intel.com>
Cc: Kamil Konieczny <kamil.konieczny@linux.intel.com>
Signed-off-by: Peter Senna Tschudin <peter.senna@linux.intel.com>
Acked-by: Ryszard Knop <ryszard.knop@intel.com>