test: hds_integration_test failures with tsan #12184
Description
On master as of today, about 20% failure rate. They may have a common root cause but there are different classes of symptoms. E.g. here are 4 different ones: a short assert-failure and some very lengthy tsan reports that are in gist.
[2020-07-20 18:10:50.211][313][critical][assert] [./test/integration/fake_upstream.h:365] assert failure: parented_ || allow_unexpected_disconnects_. Details: An queued upstream connection was torn down without being associated with a fake connection. Either manage the connection via waitForRawConnection() or waitForHttpConnection(), or set_allow_unexpected_disconnects(true).
See https://github.com/envoyproxy/envoy/blob/master/test/integration/README.md#unparented-upstream-connections
tsan failures: