Without these options set, test2json does not include a `Time`
field in the generated JSON;

{"Action":"run","Test":"TestCgroupNamespacesBuild"}
{"Action":"output","Test":"TestCgroupNamespacesBuild","Output":"=== RUN TestCgroupNamespacesBuild\n"}
{"Action":"output","Test":"TestCgroupNamespacesBuild","Output":"--- PASS: TestCgroupNamespacesBuild (1.70s)\n"}
...
{"Action":"pass","Test":"TestCgroupNamespacesBuild"}

As a result, `gotestsum` was not able to calculate test-duration, and
reported `time="0.000000"` for all tests;

<testcase classname="amd64.integration.build" name="TestCgroupNamespacesBuild" time="0.000000"></testcase>

With this patch applied:

{"Time":"2019-08-23T22:42:41.644361357Z","Action":"run","Package":"amd64.integration.build","Test":"TestCgroupNamespacesBuild"}
{"Time":"2019-08-23T22:42:41.644367647Z","Action":"output","Package":"amd64.integration.build","Test":"TestCgroupNamespacesBuild","Output":"=== RUN TestCgroupNamespacesBuild\n"}
{"Time":"2019-08-23T22:42:44.926933252Z","Action":"output","Package":"amd64.integration.build","Test":"TestCgroupNamespacesBuild","Output":"--- PASS: TestCgroupNamespacesBuild (3.28s)\n"}
...
{"Time":"2019-08-23T22:42:44.927003836Z","Action":"pass","Package":"amd64.integration.build","Test":"TestCgroupNamespacesBuild","Elapsed":3.28}

Which now correctly reports the test's duration:

<testcase classname="amd64.integration.build" name="TestCgroupNamespacesBuild" time="3.280000"></testcase>

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>