envoy hot restart possible race

# epoch 0 starts
I0307 22:28:20.091076       1 agent.go:139] Envoy starting: [-c /etc/envoy/envoy-rev0.json --restart-epoch 0 --drain-time-s 30 --parent-shutdown-time-s 45 --service-cluster istio-proxy --service-node 10.0.0.143]
[2017-03-07 22:28:20.135][18][warning][main] initializing epoch 0 (hot restart version=4.2490504)
[2017-03-07 22:28:20.138][18][warning][main] starting main dispatch loop

# epoch 1 starts
I0307 22:28:20.493637       1 agent.go:139] Envoy starting: [-c /etc/envoy/envoy-rev1.json --restart-epoch 1 --drain-time-s 30 --parent-shutdown-time-s 45 --service-cluster istio-proxy --service-node 10.0.0.143]
[2017-03-07 22:28:20.499][21][warning][main] initializing epoch 1 (hot restart version=4.2490504)
[2017-03-07 22:28:20.499][18][warning][main] shutting down admin due to child startup
[2017-03-07 22:28:20.499][18][warning][main] terminating parent process
[2017-03-07 22:28:20.526][21][warning][main] starting main dispatch loop

# epoch 2 starts
I0307 22:28:21.090821       1 agent.go:139] Envoy starting: [-c /etc/envoy/envoy-rev2.json --restart-epoch 2 --drain-time-s 30 --parent-shutdown-time-s 45 --service-cluster istio-proxy --service-node 10.0.0.143]
[2017-03-07 22:28:21.096][22][warning][main] initializing epoch 2 (hot restart version=4.2490504)
[2017-03-07 22:28:21.097][21][warning][main] shutting down admin due to child startup
[2017-03-07 22:28:21.097][21][warning][main] terminating parent process
[2017-03-07 22:28:21.097][18][warning][main] shutting down due to child request
[2017-03-07 22:28:21.097][18][warning][main] caught SIGTERM
[2017-03-07 22:28:21.097][18][warning][main] main dispatch loop exited
[2017-03-07 22:28:21.097][18][warning][main] exiting

# epoch 0 exits
I0307 22:28:21.099647       1 agent.go:189] Envoy epoch 0 process exited
[2017-03-07 22:28:21.131][22][warning][main] starting main dispatch loop
[2017-03-07 22:28:21.209][22][warning][main] all clusters initialized. initializing init manager
[2017-03-07 22:28:21.214][22][warning][main] all dependencies initialized. starting workers
[2017-03-07 22:28:21.216][21][warning][main] closing and draining listeners

# epoch 1 crashes
[2017-03-07 22:28:21.589][21][warning][main] all clusters initialized. initializing init manager
[2017-03-07 22:28:21.624][21][warning][main] all dependencies initialized. starting workers
[2017-03-07 22:28:21.626][21][critical][assert] assert failure: rc != -1: external/envoy_git/source/exe/hot_restart.cc:261
I0307 22:28:21.628570       1 agent.go:187] Envoy epoch 1 terminated: signal: aborted

# epoch 2 crashes
[2017-03-07 22:28:26.134][22][critical][assert] assert failure: rc != -1: external/envoy_git/source/exe/hot_restart.cc:261
I0307 22:28:26.136368       1 agent.go:187] Envoy epoch 2 terminated: signal: aborted