Errors in sequencer aren't easily visible/exported anywhere

```
$ go test -v github.com/google/trillian/integration
=== RUN TestLiveLogIntegration
--- SKIP: TestLiveLogIntegration (0.00s)
log_integration_test.go:50: Log integration test skipped as no tree ID provided
=== RUN TestInProcessLogIntegration
E0711 11:45:35.614068 18160 log_operation_manager.go:388] failed to execute operation on logs: failed to retrieve full list of log IDs: failed to get tx for retrieving logIDs: context canceled
--- PASS: TestInProcessLogIntegration (17.52s)
=== RUN TestInProcessLogIntegrationDuplicateLeaves
*** Test killed: ran too long (10m0s).
FAIL github.com/google/trillian/integration 600.600s
```
MySQL 5.7 server installed using developer configuration.