eg. http://logs.openstack.org/45/454545/3/check/gate-tempest-dsvm-tap-as-a-service/b29a050/logs/devstacklog.txt.gz
2017-05-15 01:23:35.024 | ++ /opt/stack/new/tap-as-a-service/devstack/plugin.sh:start_taas_openvswitch_agent:45 : run_process taas_openvswitch_agent 'python /usr/local/bin/neutron-taas-openvswitch-agent --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/taas.ini'
2017-05-15 01:23:35.025 | ++ functions-common:run_process:1564 : local service=taas_openvswitch_agent
2017-05-15 01:23:35.027 | ++ functions-common:run_process:1565 : local 'command=python /usr/local/bin/neutron-taas-openvswitch-agent --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/taas.ini'
2017-05-15 01:23:35.028 | ++ functions-common:run_process:1566 : local group=
2017-05-15 01:23:35.030 | ++ functions-common:run_process:1567 : local user=
2017-05-15 01:23:35.031 | ++ functions-common:run_process:1569 : local name=taas_openvswitch_agent
2017-05-15 01:23:35.033 | ++ functions-common:run_process:1571 : time_start run_process
2017-05-15 01:23:35.035 | ++ functions-common:time_start:2489 : local name=run_process
2017-05-15 01:23:35.036 | ++ functions-common:time_start:2490 : local start_time=
2017-05-15 01:23:35.038 | ++ functions-common:time_start:2491 : [[ -n '' ]]
2017-05-15 01:23:35.041 | +++ functions-common:time_start:2494 : date +%s
2017-05-15 01:23:35.045 | ++ functions-common:time_start:2494 : _TIME_START[$name]=1494811415
2017-05-15 01:23:35.047 | ++ functions-common:run_process:1572 : is_service_enabled taas_openvswitch_agent
2017-05-15 01:23:35.062 | ++ functions-common:is_service_enabled:2178 : return 0
2017-05-15 01:23:35.063 | ++ functions-common:run_process:1573 : [[ True = \T\r\u\e ]]
2017-05-15 01:23:35.065 | ++ functions-common:run_process:1574 : _run_under_systemd taas_openvswitch_agent 'python /usr/local/bin/neutron-taas-openvswitch-agent --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/taas.ini' '' ''
2017-05-15 01:23:35.067 | ++ functions-common:_run_under_systemd:1513 : local service=taas_openvswitch_agent
2017-05-15 01:23:35.069 | ++ functions-common:_run_under_systemd:1514 : local 'command=python /usr/local/bin/neutron-taas-openvswitch-agent --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/taas.ini'
2017-05-15 01:23:35.071 | ++ functions-common:_run_under_systemd:1515 : local 'cmd=python /usr/local/bin/neutron-taas-openvswitch-agent --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/taas.ini'
2017-05-15 01:23:35.072 | ++ functions-common:_run_under_systemd:1517 : _common_systemd_pitfalls 'python /usr/local/bin/neutron-taas-openvswitch-agent --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/taas.ini'
2017-05-15 01:23:35.074 | ++ functions-common:_common_systemd_pitfalls:1485 : local 'cmd=python /usr/local/bin/neutron-taas-openvswitch-agent --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/taas.ini'
2017-05-15 01:23:35.076 | ++ functions-common:_common_systemd_pitfalls:1488 : [[ python /usr/local/bin/neutron-taas-openvswitch-agent --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/taas.ini =~ sudo ]]
2017-05-15 01:23:35.077 | ++ functions-common:_common_systemd_pitfalls:1499 : [[ ! python /usr/local/bin/neutron-taas-openvswitch-agent --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/taas.ini =~ ^/ ]]
2017-05-15 01:23:35.079 | ++ functions-common:_common_systemd_pitfalls:1500 : local msg=
2017-05-15 01:23:35.081 | ++ functions-common:_common_systemd_pitfalls:1506 : die 1506
2017-05-15 01:23:35.082 | ++ functions-common:die:186 : local exitcode=0
2017-05-15 01:23:35.084 | [Call Trace]
2017-05-15 01:23:35.084 | ./stack.sh:1362:run_phase
2017-05-15 01:23:35.084 | /opt/stack/new/devstack/functions-common:2001:run_plugins
2017-05-15 01:23:35.084 | /opt/stack/new/devstack/functions-common:1968:source
2017-05-15 01:23:35.084 | /opt/stack/new/tap-as-a-service/devstack/plugin.sh:81:start_taas_openvswitch_agent
2017-05-15 01:23:35.084 | /opt/stack/new/tap-as-a-service/devstack/plugin.sh:45:run_process
2017-05-15 01:23:35.084 | /opt/stack/new/devstack/functions-common:1574:_run_under_systemd
2017-05-15 01:23:35.084 | /opt/stack/new/devstack/functions-common:1517:_common_systemd_pitfalls
2017-05-15 01:23:35.084 | /opt/stack/new/devstack/functions-common:1506:die
2017-05-15 01:23:35.086 | [ERROR] /opt/stack/new/devstack/functions-common:1506
2017-05-15 01:23:36.091 | Error on exit
2017-05-15 01:23:36.415 | World dumping... see /opt/stack/new/worlddump-2017-05-15-012336.txt for details
Looking back at this, it seems nobody considers it important enough to fix it. The main point of the check is to break the stack run, that part seems to work.