The fallback mechanism in dvr ingress test was introduced
in [1] in order to allow the test to work properly on
environments where the host that is used as proxy host
does not have routing to neutron external network.
As appeared the ping check in this fallback mechanism
is working inconsistently on some environments in case
cirros image is used as default image.
This patch changes the problematic ping check to
check_connectivity function that does multiple retries
before raising an exception.
[1] https://review.opendev.org/c/x/whitebox-neutron-tempest-plugin/+/925475
Change-Id: I82a5095d31a7b9e96821a0985e1400814eda02b2