CSIT Sporadic failures - v6 tests failing

uncertain at this point, but this may be specific to our pike+oxygen+snat-conntrack
job.

https://logs.opendaylight.org/releng/jenkins092/netvirt-csit-1node-openstack-pike-upstream-stateful-snat-conntrack-oxygen/3/log.html.gz#s1-s2

I quickly (< 5m) scanned the karaf.log in the time period of the Netvirt_Vpnservice/03_basic_ipv6_vpnservice.robot
suite and after it. This message seemed nefarious:

2017-09-29 10:10:02,921 | WARN | nPool-2-worker-1 | VpnInterfaceManager | 337 - org.opendaylight.netvirt.vpnmanager-impl - 0.6.0.SNAPSHOT | processVpnInterfaceUp: VPN Interface e58b5fcc-16bc-40c0-bb64-0f832fdcf664 removal on dpn 50716796633152 for vpn 4ae8cd92-48ca-49b5-94e1-b2921a261111 by FIB did not complete on time, bailing addition ...

full karaf log:
https://logs.opendaylight.org/releng/jenkins092/netvirt-csit-1node-openstack-pike-upstream-stateful-snat-conntrack-oxygen/3/odl1_karaf.log.gz