test: Ignore failure when removing routes/rules/dns

In Github CI, the container environment is changed to use tap interface
to hold the default gateway. Nmstate does not support tap interface
which cause failure during verification on pre-test clean up.

Workaround it by ignoring failure on removing routes/rules/dns during
the pre-test setup.

Signed-off-by: Gris Ge <fge@redhat.com>

tests/integration/conftest.py

@@ -93,7 +93,8 @@ def _remove_dns_route_route_rule():
                 Route.CONFIG: [{Route.STATE: Route.STATE_ABSENT}],
             },
             RouteRule.KEY: {RouteRule.CONFIG: []},
-        }
+        },
+        verify_change=False,
     )