Changes

ttcn3-ggsn-test: ignore failure to kill osmo-ggsn

Don't fail if osmo-ggsn can't be killed at the end of a testsuite
run. This happens currently with ttcn3-ggsn-test-kernel-latest-* jobs,
in the v6_only configurations, because osmo-ggsn latest doesn't support
ipv6 yet and exits. The jenkins.sh should keep going and try other
combinations, and exit without error in the end.

Fixes: d8c51cce ("ttcn3-ggsn-test: run with multiple configurations")
Change-Id: I6f3154a9ef114f31bcb5868ee09d1ebc10f35d07