Race conditions in test suite.

[tmcgilchrist]

Sharing these observed (race condition?) errors from the test suite.

┌──────────────────────────────────────────────────────────────────────────────┐
│ [FAIL]        lwt          9   Cancel.                                       │
└──────────────────────────────────────────────────────────────────────────────┘
application [INFO] -----       : Start test-case
  capnp-rpc [INFO] vat-S       : Waiting for UNENCRYPTED connections on unix:/var/folders/_l/v2016jrx2kndvkdf6p9phy_80000gn/T/build217130.dune/capnp-rpc-test-server
  capnp-rpc [INFO] -----       : Connecting to "/var/folders/_l/v2016jrx2kndvkdf6p9phy_80000gn/T/build217130.dune/capnp-rpc-test-server"...
  capnp-rpc [INFO] vat-S       : Accepting new connection
  capnp-rpc [WARNING] -----       : Error sending messages: Unix.Unix_error(Unix.ENOTCONN, "write", "") (will shutdown connection)
   endpoint [INFO] -----       : Connection closed
  capnp-rpc [INFO] vat-S       : Connection closed
  capnp-rpc [INFO] vat-C       : Connection closed
ASSERT Check log for warnings
FAIL Check log for warnings

   Expected: `0'
   Received: `1'

Raised at Alcotest_engine__Test.check in file "src/alcotest-engine/test.ml", line 196, characters 4-261
Called from Lwt.Sequential_composition.map.create_result_promise_and_callback_if_deferred.callback in file "src/core/lwt.ml", line 1981, characters 41-46

Logs saved to `~/code/ocaml/capnp-rpc/_build/default/test-lwt/_build/_tests/capnp-rpc/lwt.009.output'.
 ──────────────────────────────────────────────────────────────────────────────

Full test results in `~/code/ocaml/capnp-rpc/_build/default/test-lwt/_build/_tests/capnp-rpc'.
1 failure! in 0.718s. 27 tests run.
Fatal error: exception Alcotest_engine__Core.Make(P)(M).Test_error

┌──────────────────────────────────────────────────────────────────────────────┐
│ [FAIL]        lwt          3   Parallel.                                     │
└──────────────────────────────────────────────────────────────────────────────┘
application [INFO] -----       : Start test-case
  capnp-rpc [INFO] vat-S       : Waiting for UNENCRYPTED connections on unix:/var/folders/_l/v2016jrx2kndvkdf6p9phy_80000gn/T/build2fdbb9.dune/capnp-rpc-test-server
  capnp-rpc [INFO] -----       : Connecting to "/var/folders/_l/v2016jrx2kndvkdf6p9phy_80000gn/T/build2fdbb9.dune/capnp-rpc-test-server"...
  capnp-rpc [INFO] vat-S       : Accepting new connection
ASSERT Ping2 response
ASSERT Ping1 response
  capnp-rpc [WARNING] -----       : Error sending messages: Unix.Unix_error(Unix.ENOTCONN, "write", "") (will shutdown connection)
   endpoint [INFO] -----       : Connection closed
  capnp-rpc [INFO] vat-S       : Connection closed
  capnp-rpc [INFO] vat-C       : Connection closed
ASSERT Check log for warnings
FAIL Check log for warnings

   Expected: `0'
   Received: `1'

Raised at Alcotest_engine__Test.check in file "src/alcotest-engine/test.ml", line 196, characters 4-261
Called from Lwt.Sequential_composition.map.create_result_promise_and_callback_if_deferred.callback in file "src/core/lwt.ml", line 1981, characters 41-46

Logs saved to `~/code/ocaml/capnp-rpc/_build/default/test-lwt/_build/_tests/capnp-rpc/lwt.003.output'.
 ──────────────────────────────────────────────────────────────────────────────

Full test results in `~/code/ocaml/capnp-rpc/_build/default/test-lwt/_build/_tests/capnp-rpc'.
1 failure! in 0.564s. 27 tests run.
Fatal error: exception Alcotest_engine__Core.Make(P)(M).Test_error